U.S. patent number 8,212,433 [Application Number 12/890,441] was granted by the patent office on 2012-07-03 for electret and electrostatic induction conversion device.
This patent grant is currently assigned to Asahi Glass Company, Limited. Invention is credited to Kimiaki Kashiwagi, Kuniko Okano.
United States Patent |
8,212,433 |
Kashiwagi , et al. |
July 3, 2012 |
Electret and electrostatic induction conversion device
Abstract
An electret having a high surface charge density, is provided
and along with an electrostatic induction conversion device
including such an electret. In some embodiments, the electret
includes a laminate having a layer (A) containing a polymer
compound (a) having a relative dielectric constant of from 1.8 to
3.0 and a layer (B) containing a polymer compound (b) or inorganic
substance (c) having a relative dielectric constant higher than the
polymer compound (a). The difference between the relative
dielectric constant of the polymer compound (b) or inorganic
substance (c) and the relative dielectric constant of the polymer
compound (a) is at least 0.3. The layer (A) is disposed on the
outermost surface on a side opposite to the side where electric
charge is injected at the time of injecting electric charge into
the laminate to form the electret; and the layer (B) has a
thickness of at least 1 .mu.m.
Inventors: |
Kashiwagi; Kimiaki (Tokyo,
JP), Okano; Kuniko (Tokyo, JP) |
Assignee: |
Asahi Glass Company, Limited
(Tokyo, JP)
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Family
ID: |
41113868 |
Appl.
No.: |
12/890,441 |
Filed: |
September 24, 2010 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20110012438 A1 |
Jan 20, 2011 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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PCT/JP2009/055979 |
Mar 25, 2009 |
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Foreign Application Priority Data
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Mar 27, 2008 [JP] |
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2008-082532 |
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Current U.S.
Class: |
307/400 |
Current CPC
Class: |
H01G
7/02 (20130101); H01G 7/023 (20130101); H04R
19/016 (20130101) |
Current International
Class: |
G11C
99/00 (20060101) |
Field of
Search: |
;307/400 |
References Cited
[Referenced By]
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WO |
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Other References
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Primary Examiner: Amrany; Adi
Attorney, Agent or Firm: Foley & Lardner LLP
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
The present application is a continuation of International Patent
Application PCT/JP2009/055979 filed Mar. 25, 2009 which claims
benefit of Japanese Patent Application No. 2008-082532, filed Mar.
27, 2008.
Claims
What is claimed is:
1. An electret comprising a laminate wherein a layer (A) containing
a polymer compound (a) having a relative dielectric constant of
from 1.8 to 3.0 and a layer (B) containing a polymer compound (b)
having a relative dielectric constant higher than the polymer
compound (a) are directly laminated, wherein the difference between
the relative dielectric constant of the polymer compound (b) and
the relative dielectric constant of the polymer compound (a) is at
least 0.3; the layer (A) is disposed on the outermost surface on a
side opposite to the side where electric charge is injected at the
time of injecting electric charge into the laminate to form the
electret; and the layer (B) has a thickness of at least 1 .mu.m;
wherein the polymer compound (a) is a fluorinated polymer having an
alicyclic structure, wherein the fluorinated polymer is at least
one member selected from the list consisting of: (i) a polymer
having a unit based on a cyclic fluorinated monomer, and (ii) a
polymer having a unit formed by cyclopolymerization of a diene type
fluorinated monomer; wherein the layer (A) consists essentially of
the polymer compound (a) and a silane coupling agent; and wherein
the polymer compound (b) is at least one member selected from the
group consisting of: a polyimide, a polyparaxylylene resin, a
polycarbonate, a polyarylene, a polyarylene ether, a polyether
sulfone, and a polysulfone.
2. The electret according to claim 1, wherein the polymer compound
(b) has a glass transition temperature or melting point of at least
80.degree. C.
3. The electret according to claim 1, wherein the laminate is a
(n.sub.A+n.sub.B) layered laminate wherein n.sub.A layers of layer
A and n.sub.B layers of layer B are alternately laminated, wherein
n.sub.A is an integer of from 1 to 5, n.sub.B is an integer of from
1 to 5, and the value of n.sub.A-n.sub.B is 0 or 1.
4. An electrostatic induction conversion device comprising the
electret as defined in claim 1.
5. The electret according to claim 1, wherein the laminate is
selected from the group consisting of: a laminate comprising a
substrate, a layer (A) disposed on and in direct contact with the
substrate, and layer (B) disposed on and in direct contact with
layer (A); a laminate comprising a substrate, with layer (A)
disposed on and in direct contact with the substrate, and layer (B)
disposed on and in direct contact with layer (A), and a layer (A')
physically separated from and made of the same material as layer
(A) and disposed on and in direct contact with layer (B); and a
laminate comprising a substrate, with layer (A) disposed on and in
direct contact with the substrate, and layer (B) disposed on and in
direct contact with layer (A), a layer (A') physically separated
from and made of the same material as later (A) and disposed on and
in direct contact with layer (B), and a layer (B') physically
separated from and made of the same material as layer (B) and
disposed on and in direct contact with layer (A').
6. The electret according to claim 5, wherein the laminate
comprises at least one member selected from the group consisting of
gold, platinum, copper, aluminum, chromium, nickel, glass,
polyethylene terephthalate, polyimide, polycarbonate, an acrylic
resin and silicon.
7. The electret according to claim 1, wherein the polymer compound
(a) is a fluorinated polymer that is (i) a polymer having a unit
based on a cyclic fluorinated monomer, and wherein the cyclic
fluorinated monomer is at least one member selected from the list
consisting of: a monomer having a polymerizable double bond between
carbon atoms constituting a fluorinated alicyclic ring, and a
monomer having a polymerizable double bond between a carbon atom,
constituting a fluorinated alicyclic ring and a carbon atom of
other than a fluorinated alicyclic ring.
8. The electret according to claim 7, wherein the cyclic
fluorinated monomer comprises a compound of the formula:
##STR00021## wherein X.sup.11, X.sup.12, X.sup.13, X.sup.14, are
independent of one another, and each is at least one member
selected from the group consisting of: a fluorine atom, a
perfluoroalkyl group, and a perfluoroalkoxy group.
9. The electret according to claim 7, wherein the cyclic
fluorinated monomer comprises a compound of the formula:
##STR00022## wherein Y.sup.11 and Y.sup.12 are independent of one
another, and each is at least one member selected from the group
consisting of: a fluorine atom, a perfluoroalkyl group, and a
perfluoroalkoxy group.
10. The electret according to claim 1, wherein the polymer compound
(a) is a fluorinated polymer that is (ii) a polymer having a unit
formed by cyclopolymerization of a diene type fluorinated monomer,
wherein the diene type fluorinated monomer comprises a compound of
the formula: CF.sub.2.dbd.CF-Q-CF.dbd.CF.sub.2 wherein Q is a
C.sub.1-3 perfluoroalkylene group.
11. The electret according to claim 10, wherein Q is a C.sub.1-3
perfluoroalkylene group having an etheric oxygen atom.
12. The electret according to claim 10, wherein Q is a C.sub.1-3
perfluoroalkylene group wherein one or more fluorine atoms are
substituted by halogen atoms other than fluorine atoms.
13. The electret according to claim 1, wherein the polymer compound
(a) has a carboxyl group at a terminal of a main chain or at a side
chain.
Description
TECHNICAL FIELD
The present invention relates to an electret and an electrostatic
induction conversion device comprising such an electret.
BACKGROUND ART
Heretofore, an electrostatic induction conversion device such as a
power-generating unit or a microphone has been proposed wherein an
electret having an electric charge injected to an insulating
material, is used.
As the material for such an electret, it has been common to use a
chain polymer such as polycarbonate, polypropylene or
polytetrafluoroethylene. Further, recently, it has been proposed to
use a polymer having a fluoroalicyclic structure in its main chain
(e.g. Patent Document 1), or a cycloolefin polymer (e.g. Patent
Documents 2 and 3), as the material for such an electret. Patent
Document 1: JP-A-2006-180450 Patent Document 2: JP-A-2002-505034
Patent Document 3: JP-A-8-41260
DISCLOSURE OF THE INVENTION
Object to be Accomplished by the Invention
With respect to an electret, further improvement in its surface
charge density is desired in order to improve the conversion
efficiency between electrical energy and kinetic energy in an
electrostatic induction conversion device employing such an
electret.
The present invention has been made in view of such a conventional
problem, and it is an object of the present invention to provide an
electret having a high surface charge density and an electrostatic
induction conversion device comprising such an electret.
Means to Accomplish the Object
A first embodiment of the present invention to accomplish the above
object is an electret comprising a laminate wherein a layer (A)
containing a polymer compound (a) having a relative dielectric
constant of from 1.8 to 3.0 and a layer (B) containing a polymer
compound (b) or inorganic substance (c) having a relative
dielectric constant higher than the polymer compound (a) are
directly laminated, wherein the difference between the relative
dielectric constant of the polymer compound (b) or inorganic
substance (c) and the relative dielectric constant of the polymer
compound (a) is at least 0.3; the layer (A) is disposed on the
outermost surface on a side opposite to the side where electric
charge is injected at the time of injecting electric charge into
the laminate to form the electret; and the layer (B) has a
thickness of at least 1 .mu.m.
A second embodiment of the present invention is an electrostatic
induction conversion device comprising the electret of the first
embodiment.
Advantageous Effects of the Invention
According to the present invention, it is possible to provide an
electret having a high surface voltage and a process for its
production as well as an electrostatic induction conversion device
comprising such an electret, whereby the conversion efficiency
between electrical energy and kinetic energy is improved.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram illustrating a corona charging
equipment used for injection of electric charge.
FIG. 2 is a diagram showing set positions for measuring points for
surface voltages.
MEANINGS OF SYMBOLS
10: copper substrate, 11: laminate, 12: DC high-voltage power
source, 14: corona needle, 16: grid, 17: ammeter, 18: power source
for grid, 19: hot plate
BEST MODE FOR CARRYING OUT THE INVENTION
Now, the present invention will be described in further detail.
In the following specification, "repeating units" constituting a
polymer may be referred to simply as "units".
Further, a unit represented by the formula (a1) may be referred to
also as "a unit (a1)". A unit, compound or the like represented by
another formula will be referred to in a similar manner, and for
example, a monomer represented by the formula (1) may be referred
to also as "a monomer (1)".
The electret of the present invention is characterized in that it
comprises a laminate wherein the following layers (A) and (B) are
directly laminated. In such a laminate, the layer (A) is disposed
on the outermost surface on a side opposite to the side where
electric charge is injected at the time of injecting electric
charge into the laminate to form an electret.
Layer (A): a layer containing a polymer compound (a) having a
relative dielectric constant of from 1.8 to 3.0.
Layer (B): a layer containing a polymer compound (b) or inorganic
substance (c) having a relative dielectric constant higher by at
least 0.3 than the relative dielectric constant of the polymer
compound (a), and having a thickness of at least 1 .mu.m.
The layer (A) is a portion which plays a role for charge retention
as an electret.
The layer (B) is in contact directly with the layer (A) so as to
contribute to the improvement of the surface charge density.
<Layer (A)>
The layer (A) is constituted by a polymer compound (a) having a
relative dielectric constant of from 1.8 to 3.0. The relative
dielectric constant is preferably from 1.8 to 2.7, more preferably
from 1.8 to 2.3. When the relative dielectric constant is at least
the lower limit within the above range, the amount of electric
charge which can be stored as an electret will be high, and when it
is lower than the upper limit, the electrical insulation property
and the charge retention stability as an electret will be
excellent.
Further, since the layer (A) is a portion which plays a role for
charge retention as an electret, as the polymer compound (a), one
having a high volume resistivity and a high dielectric breakdown
strength is preferably employed.
The volume resistivity of the polymer compound (a) is preferably
from 10.sup.10 to 10.sup.20 .OMEGA.cm, more preferably from
10.sup.16 to 10.sup.19 .OMEGA.cm. The volume resistivity is
measured by ASTM D257.
Further, the dielectric breakdown strength of the polymer compound
(a) is preferably from 10 to 25 kV/mm, more preferably from 15 to
22 kV/mm. The dielectric breakdown strength is measured by ASTM
D149.
The polymer compound (a) is not particularly limited so long as the
relative dielectric constant is within the above range. For
example, it may optionally be selected from polymer compounds which
have been used for electrets.
In the present invention, as the polymer compound (a), one having
an alicyclic structure is preferred, since it is excellent in the
charge retention performance.
The "alicyclic structure" means a cyclic structure having no
aromatic nature. The alicyclic structure may, for example, be a
saturated or unsaturated hydrocarbon cyclic structure which may
have a substituent, a heterocyclic structure having some of carbon
atoms in such a hydrocarbon cyclic structure substituted by hetero
atoms such as oxygen atoms or nitrogen atoms, or a fluorinated
alicyclic structure having hydrogen atoms in such a hydrocarbon
cyclic structure or heterocyclic structure substituted by fluorine
atoms.
The polymer compound having such an alicyclic structure may, for
example, be a cycloolefin polymer.
The "cycloolefin polymer" is a polymer having an aliphatic
hydrocarbon cyclic structure in the main chain of the polymer and
is meant for one wherein at least two among carbon atoms
constituting such an aliphatic hydrocarbon cyclic structure are
incorporated in the main chain of the polymer.
The cycloolefin polymer has a unit having an aliphatic hydrocarbon
cyclic structure (hereinafter sometimes referred to as a unit
(a1)), and in such a unit (a1), at least two among carbon atoms
constituting such an aliphatic hydrocarbon cyclic structure are
incorporated in the main chain of the polymer. As the cycloolefin
polymer, preferred may be one containing the following unit
(a1-1):
##STR00001## wherein R is a bivalent hydrocarbon group which may
have a substituent, m is an integer of from 0 to 10, r is an
integer of 0 or 1, and s is an integer of 0 or 1.
In the formula (a1-1), the hydrocarbon group for R "may have a
substituent", which means that some or all of hydrogen atoms in the
hydrocarbon group may be substituted by substituents.
Such a substituent may, for example, be an alkyl group, a
cycloalkyl group, an alkoxy group, an aryl group such as a phenyl
group, or a polycyclic aliphatic hydrocarbon group such as an
adamantyl group.
The alkyl group as such a substituent may be linear or branched and
has preferably from 1 to 10, more preferably from 1 to 3, carbon
atoms. Such an alkyl group is preferably a methyl group, an ethyl
group, a propyl group or an isopropyl group, particularly
preferably a methyl group or an ethyl group.
The cycloalkyl group as such a substituent has preferably from 3 to
10, more preferably from 5 to 8, carbon atoms. Such a cycloalkyl
group is particularly preferably a cyclopentyl group or a
cyclohexyl group.
The alkoxy group as such a substituent may, for example, be one
having an oxygen atom (--O--) bonded to the above alkyl group.
The hydrocarbon group for R may be in a chain form or cyclic.
Further, such a hydrocarbon group may be saturated or unsaturated,
preferably saturated.
The chain form hydrocarbon group is preferably a linear alkylene
group which may have a substituent, and it has preferably from 1 to
4, more preferably from 2 to 3, most preferably 2, carbon atoms.
Specifically, a dimethylene group may be mentioned.
The cyclic hydrocarbon group is preferably a group having two
hydrogen atoms removed from a monocyclic or polycyclic cycloalkane
which may have a substituent. The monocyclic cycloalkane may, for
example, be cyclopentane or cyclohexane. The polycyclic cycloalkane
may, for example, be norbornane or adamantane. Among them,
cyclopentane or norbornane is preferred.
In the formula (a1-1), m is an integer of from 0 to 10.
In a case where m is an integer of at least 1, as in the
after-mentioned unit (a1-11), the polymer main chain is bonded not
at the o-position but with a space or at least one methylene chain,
of the aliphatic hydrocarbon cyclic structure, so that the
aliphatic hydrocarbon cyclic structure is incorporated in the
polymer main chain. In such a case, m is preferably an integer of
from 1 to 3, most preferably 1.
When m is 0, as shown in the after-mentioned unit (a1-21), the
polymer main chain is bonded at the o-position of the aliphatic
hydrocarbon cyclic structure, so that the aliphatic hydrocarbon
cyclic structure is incorporated in the polymer main chain.
Each of r and s may be 0 or 1.
Particularly when m is 0, r and s are preferably 0. Further, when m
is 1, r and s are preferably 1.
As the unit (a1-1), preferred may, for example, be the following
unit (a1-11) or unit (a1-21).
##STR00002## wherein each of R.sup.1 and R.sup.2 which are
independent of each other, is a hydrogen atom, an alkyl group or a
cycloalkyl group, and R.sup.1 and R.sup.2 may be bonded to each
other to form a ring.
##STR00003## wherein each of R.sup.3 and R.sup.4 which are
independent of each other, is a hydrogen atom, an alkyl group or a
cycloalkyl group, or R.sup.3 and R.sup.4 may be bonded to each
other to form a ring.
In the formula (a1-11), the alkyl group or the cycloalkyl group for
R.sup.1 or R.sup.2 may, respectively, be the same one as the alkyl
group or the cycloalkyl group mentioned as the above
substituent.
R.sup.1 and R.sup.2 may be bonded to each other to form a ring
together with the carbon atoms to which R.sup.1 and R.sup.2 are
respectively bonded. In such a case, the ring to be formed is
preferably a monocyclic or polycyclic cycloalkane. The monocyclic
cycloalkane may, for example, be cyclopentane or cyclohexane. The
polycyclic cycloalkane may, for example, be norbornane or
adamantane. Among them, cyclopentane or norbornane is
preferred.
Such a ring may have a substituent. The substituent may, for
example, be the same one as the substituent which the
above-mentioned hydrocarbon group for R may have.
Specific examples of the unit (a1-11) in a case where R.sup.1 and
R.sup.2 form a ring, include the following units (a1-11-1) and
(a1-12-1).
##STR00004## wherein R.sup.11 is a hydrogen atom or an alkyl
group.
The alkyl group for R.sup.11 may, for example, be the same one as
the alkyl group mentioned as the substituent which the
above-mentioned hydrocarbon group for R may have, and particularly
preferred is a methyl group.
In the present invention, the unit (a1-11) is preferably one
wherein R.sup.1 and R.sup.2 form a ring, or one wherein at least
one of R.sup.1 and R.sup.2 is a cycloalkyl group.
In the formula (a1-21), R.sup.3 and R.sup.4 are, respectively, the
same as the above R.sup.1 and R.sup.2.
Specific examples of the unit (a1-21) in a case where R.sup.3 and
R.sup.4 form a ring, include the following units (a1-21-1) and
(a1-21-2).
##STR00005## wherein R.sup.13 is a hydrogen atom or an alkyl
group.
The alkyl group for R.sup.13 may, for example, be the same one as
the alkyl group mentioned as the substituent which the
above-mentioned hydrocarbon group for R may have, and particularly
preferred is a methyl group.
The cycloolefin polymer may contain one or more types among the
above-described units, as the unit (a1).
The proportion of the unit (a1) in the cycloolefin polymer is
preferably at least 30 mol %, more preferably at least 40 mol %, or
may be 100 mol %, based on the total of all repeating units
constituting the cycloolefin polymer.
The cycloolefin polymer may contain a unit other than the unit (a1)
(hereinafter sometimes referred to as a unit (a2)).
As the unit (a2), an optional unit which has been used for a
cycloolefin polymer, may be used without any particular
limitation.
As such a unit (a2), a unit based on an olefin which may have a
substituent, is preferred, and as such a unit, the following unit
(a2-1) may, for example, be mentioned.
##STR00006## wherein R.sup.5 is a hydrogen atom or an alkyl
group.
In the formula, the alkyl group for R.sup.5 may be the same one as
the alkyl group mentioned as the substituent which the
above-mentioned hydrocarbon group for R may have.
The cycloolefin polymer to be used in the present invention is
particularly preferably the following cycloolefin polymer (I) or
cycloolefin polymer (II).
Cycloolefin polymer (I): a cycloolefin polymer containing the above
unit (a1-11).
Cycloolefin polymer (II): a cycloolefin polymer containing the
above unit (a1-21) and the unit (a2).
The cycloolefin polymer (I) may contain one or more types as the
unit (a1-11).
Further, the cycloolefin polymer (I) may contain a unit other than
the unit (a1-11) within a range not to impair the effects of the
present invention. In the cycloolefin polymer (I), the proportion
of the unit (a1-11) is preferably at least 80 mol %, more
preferably at least 90 mol %, particularly preferably 100 mol %,
based on the total of all repeating units constituting the
cycloolefin polymer (I). That is, as the cycloolefin polymer (I), a
polymer composed solely of the unit (a1-11) is particularly
preferred.
The cycloolefin polymer (II) may contain one or more types as each
of the unit (a1-21) and the unit (a2).
Further, the cycloolefin polymer (II) may contain a unit other than
the unit (a1-21) and the unit (a2) within a range not to impair the
effects of the present invention.
In the cycloolefin polymer (II), the proportion of the unit (a1-21)
is preferably from 20 to 70 mol %, more preferably from 30 to 50
mol %, based on the total of all repeating units constituting the
cycloolefin polymer (II). Further, the proportion of the unit (a2)
is preferably from 30 to 80 mol %, more preferably from 50 to 70
mol %, based on the total of all repeating units constituting the
cycloolefin polymer (II).
Further, the content ratio (molar ratio) of the unit (a1-21) to the
unit (a2) in the cycloolefin polymer (II) is preferably within a
range of the unit (a1-21):the unit (a2)=20:80 to 70:30, more
preferably within a range of 30:70 to 50:50.
Preferred specific examples of the cycloolefin polymer (II) include
copolymers containing two types of the respective units as shown by
the following formulae (II-1) and (II-2):
##STR00007## wherein R.sup.13 and R.sup.5 are, respectively, as
defined above.
The cycloolefin polymer may have functional groups as terminal
groups at the main chain terminals and/or side chain portions.
Such a functional group may, for example, be an alkoxy carbonyl
group (which may be referred to also as an ester group), a carboxy
group, a carboxylic acid halide group, an amide group, a hydroxy
group, an amino group, a sulfonic acid group, a sulfonate group, a
sulfonamide group, a thiol group or a cyano group. Among them, an
alkoxy carbonyl group or a carboxy group is preferred.
In a case where a carboxy group is contained as a terminal group, a
silane compound may be bonded to such a carboxy group.
The silane compound may be bonded to such a carboxy group, for
example, by reacting a cycloolefin polymer having a carboxy group
at a terminal group, with a silane coupling agent which will be
described hereinafter.
A cycloolefin polymer having functional groups such as alkoxy
carbonyl groups or carboxy groups as terminal groups, may, for
example, be a modified polymer compound obtained by
graft-copolymerizing a modified monomer composed of an unsaturated
carboxylic acid and its derivative, to a cycloolefin polymer.
Such an unsaturated carboxylic acid may, for example, be acrylic
acid, methacrylic acid, .alpha.-ethylacrylic acid, maleic acid,
fumaric acid, itaconic acid, citraconic acid, nadic acid or
methylnadic acid. The derivative of such an unsaturated carboxylic
acid may, for example, be an acid halide, amide, imide, acid
anhydride or ester, of the above unsaturated carboxylic acid.
Specifically, malenyl chloride, maleic anhydride, citraconic
anhydride, methyl maleate or dimethyl maleate may, for example, be
mentioned.
The cycloolefin polymer is not particularly limited so long as it
is one which satisfies the desired characteristics such as the
relative dielectric constant. A commercially available one may be
employed, or it may the synthesized.
As methods for the synthesis of the cycloolefin polymer, the
following (1) to (7) are, for example, known.
Here, the represented unit in the final product in each reaction
formula shows a unit contained in the obtained cycloolefin
polymer.
(1) A method wherein a norbornene and an olefin are subjected to
addition copolymerization (e.g. a method shown by the following
reaction formula (1')).
(2) A method wherein a ring opened metathesis polymer of a
norbornene is subjected to hydrogenation (e.g. a method shown by
the following reaction formula (2'))
(3) A method wherein an alkylidene norbornene is subjected to
transannular polymerization (e.g. a method shown by the following
reaction formula (3')).
(4) A method wherein a norbornene is subjected to addition
polymerization (e.g. a method shown by the following reaction
formula (4')).
(5) A method wherein 1,2- and 1,4-addition polymers of
cyclopentadiene are subjected to hydrogenation (e.g. a method shown
by the following reaction formula (6)).
(6) A method wherein 1,2- and 1,4-addition polymers of
cyclohexadiene are subjected to hydrogenation (e.g. a method shown
by the following reaction formula (6')).
(7) A method wherein a conjugated diene is subjected to
cyclopolymerization (e.g. a method shown by the following reaction
formula (7')).
##STR00008## ##STR00009##
In each reaction formula, R.sup.1 to R.sup.5 are as defined
above.
Each of R.sup.6 and R.sup.7 which are independent of each other, is
an alkyl group, and such an alkyl group may be the same one as the
alkyl group mentioned as a substituent which the above-mentioned
hydrocarbon group for R may have.
Among them, preferred are a cycloolefin polymer obtainable by the
method (1) (an addition copolymer of a norbornene and an olefin)
and a cycloolefin polymer obtainable by the method (2) (a
hydrogenated polymer of a ring opened metathesis polymer of a
norbornene) in view of the excellent film-forming property and
efficiency in their syntheses.
The addition copolymer of a norbornene may, for example, be one
commercially available under a tradename of APEL (registered
trademark) (manufactured by Mitsui Chemicals Inc.) or TOPAS
(registered trademark) (manufactured by Ticona).
As the hydrogenated polymer of a ring-opened metathesis polymer of
a norbornene, various ones are available, but polymers commercially
available under tradenames of ZEONEX (registered trademark)
(manufactured by ZEON CORPORATION), ZEONOR (registered trademark)
(manufactured by ZEON CORPORATION) and ARTON (registered trademark)
(manufactured by JSR Corporation) are preferred since they have
transparency, low moisture absorption and heat resistance.
Further, as a preferred polymer compound (a), a fluororesin may be
mentioned. The fluororesin is excellent in electrical insulation
properties and also excellent in charge retention performance as an
electret. As such a fluororesin, particularly preferred is a
fluororesin having an alicyclic structure (e.g. the after-mentioned
fluorinated cyclic polymer).
The fluororesin to be used as the polymer compound (a) may
specifically be, for example, a polytetrafluoroethylene, an
ethylene/tetrafluoroethylene copolymer (ETFE), a
tetrafluoroethylene/perfluoro(alkyl vinyl ether) copolymer (PFA), a
fluoroolefin/alkyl vinyl ether copolymer or a fluorinated cyclic
polymer. Among them, from the viewpoint of electrical insulation
properties, at least one member selected from the group consisting
of a polytetrafluoroethylene, a tetrafluoroethylene/perfluoro(alkyl
vinyl ether) copolymer (PFA) and a fluorinated cyclic polymer, is
preferred, and a fluorinated cyclic polymer is particularly
preferred.
The "fluorinated cyclic polymer" is a fluoropolymer having a
fluorinated alicyclic structure in the main chain and is meant for
one wherein at least one of carbon atoms constituting the
fluorinated alicyclic structure is a carbon atom constituting the
main chain of the fluoropolymer.
Among carbon atoms constituting the fluorinated alicyclic
structure, a carbon atom constituting the main chain is derived
from the polymerizable double bond of a monomer constituting the
fluoropolymer.
For example, in a case where the fluoropolymer is a fluoropolymer
obtained by polymerizing a cyclic monomer as described hereinafter,
two carbon atoms constituting the double bond become the carbon
atoms constituting the main chain.
Further, in the case of a fluoropolymer obtained by
cyclopolymerizing a monomer having two polymerizable double bonds,
at least two among the four carbon atoms constituting the two
polymerizable double bonds become the carbon atoms constituting the
main chain.
The fluorinated alicyclic structure may be one wherein the cyclic
skeleton is constituted solely by carbon atoms, or a heterocyclic
structure wherein a hetero atom such as an oxygen atom or a
nitrogen atom is contained in addition to the carbon atoms. The
fluorinated alicyclic ring is preferably a fluorinated alicyclic
ring having one or two etheric oxygen atoms in the cyclic
skeleton.
The number of atoms constituting the cyclic skeleton of the
fluorinated alicyclic structure is preferably from 4 to 7, more
preferably from 5 to 6. That is, the fluorinated alicyclic
structure is preferably a 4- to 7-membered ring, more preferably a
5- or 6-membered ring.
As a preferred fluorinated cyclic polymer, the following
fluorinated cyclic polymer (I') or fluorinated cyclic polymer (II')
may be mentioned.
Fluorinated cyclic polymer (I'): a polymer having a unit based on a
cyclic fluorinated monomer.
Fluorinated cyclic polymer (II'): a polymer having a unit formed by
cyclopolymerization of a diene type fluorinated monomer.
The "cyclic fluorinated monomer" is a monomer having a
polymerizable double bond between carbon atoms constituting a
fluorinated alicyclic ring, or a monomer having a polymerizable
double bond between a carbon atom constituting a fluorinated
alicyclic ring and a carbon atom of other than a fluorinated
alicyclic ring.
Such a cyclic fluoromonomer is preferably a compound (1) or a
compound (2).
##STR00010##
In the above formulae, each of X.sup.11, X.sup.12, X.sup.13,
X.sup.14, Y.sup.11 and Y.sup.12 which are independent of one
another, is a fluorine atom, a perfluoroalkyl group or a
perfluoroalkoxy group.
The perfluoroalkyl group for X.sup.11, X.sup.12, X.sup.13,
X.sup.14, Y.sup.11 and Y.sup.12 has preferably from 1 to 7, more
preferably from 1 to 4, carbon atoms. Such a perfluoroalkyl group
is preferably linear or branched, more preferably linear.
Specifically, it may, for example, be a trifluoromethyl group, a
pentafluoroethyl group or a heptafluoropropyl group, and
particularly preferred is a trifluoromethyl group.
The perfluoroalkoxy group for X.sup.12, X.sup.13, X.sup.14,
Y.sup.11 and Y.sup.12 may, for example, be one having an oxygen
atom (--O--) bonded to the above perfluoroalkyl group.
X.sup.11 is preferably a fluorine atom.
X.sup.12 is preferably a fluorine atom, a trifluoromethyl group or
a C.sub.1-4 perfluoroalkoxy group, more preferably a fluorine atom
or a trifluoromethoxy group.
Each of X.sup.13 and X.sup.14 which are independent of each other,
is preferably a fluorine atom or a C.sub.1-4 perfluoroalkyl group,
more preferably a fluorine atom or a trifluoromethyl group.
Each of Y.sup.11 and Y.sup.12 which are independent of each other,
is preferably a fluorine atom, a C.sub.1-4 perfluoroalkyl group or
a C.sub.1-4 perfluoroalkoxy group, more preferably a fluorine atom
or a trifluoromethyl group.
In the compound (1), X.sup.13 and X.sup.14 may be bonded to each
other to form a fluorinated alicyclic ring together with the carbon
atoms to which X.sup.13 and X.sup.14 are bonded.
Such a fluorinated alicyclic ring is preferably a 4- to 6-membered
ring.
Such a fluorinated alicyclic ring is preferably a saturated
alicyclic ring.
Such a fluorinated alicyclic ring may have an etheric oxygen atom
(--O--) in the cyclic skeleton. In such a case, the number of
etheric oxygen atoms in the fluorinated alicyclic ring is
preferably 1 or 2.
In the compound (2), Y.sup.11 and Y.sup.12 may be bonded to each
other to form a fluorinated alicyclic ring together with the carbon
atoms to which Y.sup.11 and Y.sup.12 are bonded.
Such a fluorinated alicyclic ring is preferably a 4- to 6-membered
ring.
Such a fluorinated alicyclic ring is preferably a saturated
alicyclic ring.
Such a fluorinated alicyclic ring may have an etheric oxygen atom
(--O--) in the cyclic skeleton. In such a case, the number of
etheric oxygen atoms in the fluorinated alicyclic ring is
preferably 1 or 2.
Preferred specific examples of the compound (1) include compounds
(1-1) to (1-5).
Specific examples of the compound (2) include compounds (2-1) and
(2-3).
##STR00011##
The fluorinated cyclic polymer (I') may be a homopolymer of the
above cyclic fluorinated monomer, or may be a copolymer of such a
cyclic fluorinated monomer with another monomer.
However, in such a fluorinated cyclic polymer (I'), the proportion
of the unit based on the cyclic fluorinated monomer is preferably
at least 20 mol %, more preferably at least 40 mol %, or may be 100
mol %, based on the total of all repeating units constituting the
fluorinated cyclic polymer (I').
Said another monomer may be one copolymerizable with the above
cyclic fluorinated monomer and is not particularly limited.
Specifically, the after-mentioned diene-type fluorinated monomer,
tetrafluoroethylene, chlorotrifluoroethylene or perfluoro(methyl
vinyl ether) may, for example, be mentioned.
The "diene-type fluorinated monomer" is a monomer having two
polymerizable double bonds and fluorine atoms. Such polymerizable
double bonds are not particularly limited, but preferably vinyl
groups, allyl groups, acryloyl groups or methacryloyl groups.
The diene-type fluorinated monomer is preferably a compound (3).
CF.sub.2.dbd.CF-Q-CF.dbd.CF.sub.2 (3)
In the formula, Q is a C.sub.1-3 perfluoroalkylene group which may
have an etheric oxygen atom and wherein some of fluorine atoms may
be substituted by halogen atoms other than fluorine atoms. Such
halogen atoms other than fluorine atoms may, for example, be
chlorine atoms or bromine atoms.
In a case where Q is a perfluoroalkylene group having an etheric
oxygen atom, the etheric oxygen atom in the perfluoroalkylene group
may be present at one terminal of the group or may be present at
both terminals of the group, or may be present between carbon atoms
of the group. From the viewpoint of the cyclopolymerizability, it
is preferably present at one terminal of the group.
As the unit to be formed by cyclopolymerization of the compound
(3), repeating units of the following formulae (3-1) to (3-4) may
be mentioned.
##STR00012##
The following compounds may be mentioned as specific examples of
the compound (3).
CF.sub.2.dbd.CFOCF.sub.2CF.dbd.CF.sub.2,
CF.sub.2.dbd.CFOCF(CF.sub.3)CF.dbd.CF.sub.2,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.dbd.CF.sub.2,
CF.sub.2.dbd.CFOCF.sub.2CF(CF.sub.3)CF.dbd.CF.sub.2,
CF.sub.2.dbd.CFOCF(CF.sub.3)CF.sub.2CF.dbd.CF.sub.2,
CF.sub.2.dbd.CFOCFClCF.sub.2CF.dbd.CF.sub.2,
CF.sub.2.dbd.CFOCCl.sub.2CF.sub.2CF.dbd.CF.sub.2,
CF.sub.2.dbd.CFOCF.sub.2OCF.dbd.CF.sub.2,
CF.sub.2.dbd.CFOC(CF.sub.3).sub.2OCF.dbd.CF.sub.2,
CF.sub.2.dbd.CFOCF.sub.2CF(OCF.sub.3)CF.dbd.C F.sub.2,
CF.sub.2.dbd.CFCF.sub.2CF.dbd.CF.sub.2,
CF.sub.2.dbd.CFCF.sub.2CF.sub.2CF.dbd.CF.sub.2,
CF.sub.2.dbd.CFCF.sub.2OCF.sub.2CF.dbd.CF.sub.2, etc.
The fluorinated cyclic polymer (II') may be constituted solely by a
unit formed by cyclopolymerization of the above diene-type
fluoromonomer, or may be a copolymer of such a unit with another
unit.
However, in such a fluorinated cyclic polymer (II'), the proportion
of the unit formed by cyclopolymerization of the diene-type
fluorinated monomer is preferably at least 50 mol %, more
preferably at least 80 mol %, most preferably 100 mol %, based on
the total of all repeating units constituting the fluorinated
cyclic polymer (II').
Said another monomer may be one copolymerizable with the above
diene-type fluorinated monomer and is not particularly limited.
Specifically, a cyclic fluorinated monomer such as the
above-mentioned compound (1) or (2), tetrafluoroethylene,
chlorotrifluoroethylene, or perfluoro(methyl vinyl ether) may, for
example, be mentioned.
The weight average molecular weight of the polymer compound (a) is
preferably from 3,000 to 1,000,000, more preferably from 10,000 to
300,000.
Further, the polymer compound (a) preferably has a glass transition
temperature of at least 80.degree. C., more preferably at least
100.degree. C. When the glass transition temperature is at least
100.degree. C., the electret will be excellent in heat resistance,
stability of maintained charge. Further, such a glass transition
temperature is preferably at most 350.degree. C., more preferably
at most 250.degree. C., most preferably at most 200.degree. C., in
consideration of e.g. the film-forming property at the time of
forming the polymer compound (a) into a film or the solubility of
the polymer compound (a) in a solvent.
The glass transition temperature of the polymer compound (a) can be
adjusted by adjusting the types or proportions of the repeating
units constituting the polymer compound (a). For example, in the
case of the above fluorinated cyclic polymer, the repeating units
based on the above compound (1) or (2) contribute to an improvement
of the glass transition temperature of the polymer, and the larger
the proportion of such units, the higher the glass transition
temperature.
As the fluororesin, one satisfying the desired properties such as
the above relative dielectric constant may suitably be selected
from commercial products, or may be synthesized by a usual
method.
For example, a fluorinated cyclic polymer may be produced by
carrying out e.g. cyclopolymerization, homopolymerization or
copolymerization of monomers for the respective units by applying a
conventional method disclosed in e.g. JP-A-4-189880.
Further, as commercial products of the fluorinated cyclic polymer,
CYTOP (registered trademark) (manufactured by Asahi Glass Company,
Limited), Teflon (registered trademark) AF (manufactured by Du
Pont) and HYFLON (registered trademark) AD (manufactured by Solvey
Solexis) may, for example, be mentioned.
A method for forming the layer (A) is not particularly limited.
However, as a preferred method, a method may, for example, be
mentioned wherein the polymer compound (a) is dissolved in a
solvent to prepare a coating composition, and by using such a
coating composition, a coating film is formed.
Such forming of a coating film may be carried out, for example, by
coating a substrate or the surface of the layer (B) with the
coating composition, followed by drying by e.g. baking. As the
coating method, a conventional method for forming a film from a
solution may be used without any particular limitation. Specific
examples of such a method include, for example, a roll coater
method, a casting method, a dipping method, a spin coating method,
a casting-on-water method, a Lanmuir.cndot.Blodgett method, a die
coating method, an inkjet method and a spray coating method.
Otherwise, it is possible to employ a printing technique such as a
relief printing method, a gravure printing method, a lithography
method, a screen printing method or a flexo printing method.
A solvent for the coating composition is not particularly limited
so long as it is one capable of dissolving the polymer compound (a)
and forming a coating film having a desired thickness and
uniformity by a desired coating method, and it may, for example, be
a protic solvent or an aprotic solvent.
The protic solvent may, for example, be methanol, ethanol,
1-propanol, isopropyl alcohol, 1-butanol, 2-butanol, t-butanol,
pentanol, hexanol, 1-octanol, 2-octanol, ethylene glycol, ethylene
glycol monomethyl ether, propylene glycol monomethyl ether,
propylene glycol monobutyl ether, propylene glycol, methyl lactate
or the after-mentioned protic fluorinated solvent.
The aprotic solvent may, for example, be hexane, cyclohexane,
heptane, octane, decane, dodecane, decalin, acetone, cyclohexanone,
2-butanone, dimethoxyethane, monomethyl ether, ethyl acetate, butyl
acetate, diglyme, triglyme, propylene glycol monomethyl ether
monoacetate (PGMEA), N,N-dimethylformamide (DMF),
N,N-dimethylacetamide (DMA), N-methylpyrrolidone, tetrahydrofuran,
anisole, dichloromethane, dichloroethane, chloroform, carbon
tetrachloride, chlorobenzene, dichlorobenzene, benzene, toluene,
xylene, ethylbenzene, mesitylene, tetralin, methylnaphthalene, or
the after-mentioned aprotic fluorinated solvent.
These solvents may be used alone or in combination as a mixture of
two or more of them. Further, a wide range of compounds may be used
other than these solvents.
Among them, in a case where a cycloolefin polymer is used as the
polymer compound (a), as the solvent, an aprotic solvent is
preferred, a hydrocarbon is more preferred, an aromatic hydrocarbon
such as benzene, toluene, xylene, ethylbenzene, mesitylene,
tetralin or methylnaphthalene is further preferred, and toluene or
xylene is particularly preferred.
Further, in a case where a fluororesin is used as the polymer
compound (a), as the solvent, an aprotic solvent is preferred, and
an aprotic fluorinated solvent is more preferred.
As the aprotic fluorinated solvent, preferred may, for example, be
the following fluorinated compounds.
A fluorinated aromatic compound such as hexafluoromethaxylylene,
fluorobenzene, difluorobenzene, perfluorobenzene,
pentafluorobenzene, 1,3-bis(trifluoromethyl)benzene or
1,4-bis(trifluoromethyl)benzene; a perfluorotrialkylamine compound
such as perfluorotributylamine or perfluorotripropylamine; a
perfluorocycloalkane compound such as perfluorodecalin,
perfluorocyclohexane or perfluoro(1,3,5-trimethylcyclohexane); a
perfluorocyclic ether compound such as
perfluoro(2-butyltetrahydrofuran); a low molecular weight
perfluoropolyether; a perfluoroalkane such as perfluorohexane,
perfluorooctane, perfluorodecane, perfluorododecane,
perfluoro(2,7-dimethyloctane), perfluoro(1,2-dimethylhexane) or
perfluoro(1,3-dimethylhexane); a chlorofluorocarbon such as
1,1,2-trichloro-1,2,2,-trifluoroethane,
1,1,1-trichloro-2,2,2-trifluoroethane,
1,3-dichloro-1,1,2,2,3-pentafluoropropane,
1,1,1,3-tetrachloro-2,2,3,3-tetrafluoropropane or
1,1,3,4-tetrachloro-1,2,2,3,4,4-hexafluorobutane; a
hydrofluorocarbon such as 1,1,1,2,2,3,3,5,5,5-decafluoropentane,
1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorohexane,
1,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8-heptadecafluorooctane,
1,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10-henicosafluorodecane,
1,1,1,2,2,3,3,4,4-nonafluorohexane,
1,1,1,2,2,3,3,4,4,5,5,6,6-tridecafluorooctane,
1,1,1,2,2,3,3,4,4,5,5,6,6,7,7,8,8-heptadecafluorodecane,
1,1,1,2,3,4,5,5,5-nonafluoro-4-(trifluoromethyl)pentane or
1,1,1,2,2,3,5,5,5-nonafluoro-4-(trifluoromethyl)pentane; and a
hydrochlorofluorocarbon such as
3,3-dichloro-1,1,1,2,2-pentafluoropropane or
1,3-dichloro-1,1,2,2,3-pentafluoropropane.
These fluorinated compounds may be used alone or in combination as
a mixture of two or more of them.
Further, a wide range of aprotic fluorinated solvents other than
the above may, also be used.
For example, a fluorinated solvent such as hydrofluoroether (HFE)
is preferred. Such a fluorinated solvent is a fluorinated solvent
(hereinafter sometimes referred to as a fluorinated solvent (2))
represented by the general formula R.sup.1--O--R.sup.2 (wherein
R.sup.1 is a C.sub.5-12 linear or branched polyfluoroalkyl group
which may have an etheric oxygen atom, and R.sup.2 is a C.sub.1-5
linear or branched alkyl group or a polyfluoroalkyl group).
The polyfluoroalkyl group for R.sup.1 is a group wherein at least
two hydrogen atoms in an alkyl group are substituted by fluorine
atoms and includes a perfluoroalkyl group wherein all hydrogen
atoms in an alkyl group are substituted by fluorine atoms and a
group wherein at least two hydrogen atoms in an alkyl group are
substituted by fluorine atoms and at least one hydrogen atom in the
alkyl group is substituted by a halogen atom other than a fluorine
atom. The halogen atom other than a fluorine atom is preferably a
chlorine atom.
The polyfluoroalkyl group is preferably a group wherein at least
60%, more preferably at least 80%, by number of hydrogen atoms in
the corresponding alkyl group are substituted by fluorine atoms. A
more preferred polyfluoroalkyl group is a perfluoroalkyl group.
In a case where R.sup.1 has an etheric oxygen atom, if the number
of etheric oxygen atoms is too large, the solubility will be
impaired, and therefore, the number of etheric oxygen atoms in
R.sup.1 is preferably from 1 to 3, more preferably from 1 to 2.
When the number of carbon atoms in R.sup.1 is at least 5, the
solubility of the fluorinated polymer will be good, and when the
number of carbon atoms in R.sup.1 is at most 12, such a polymer is
readily industrially available. Accordingly, the number of carbon
atoms in R.sup.1 is selected within a range of from 5 to 12. The
number of carbon atoms in R.sup.1 is preferably from 6 to 10, more
preferably from 6 to 7 and from 9 to 10.
The number of carbon atoms in R.sup.2 is from 1 to 5, and when the
number of carbon atoms is at most 5, the solubility of the
fluorinated polymer will be good. A preferred example of R.sup.2 is
a methyl group or an ethyl group.
The molecular weight of the fluorinated solvent (2) is preferably
at most 1,000, since if it is too large, not only the viscosity of
the fluorinated polymer composition is likely to increase but also
the solubility of the fluorinated polymer decreases.
Further, the fluorine content of the fluorinated solvent (2) is
preferably from 60 to 80 mass %, whereby the fluorinated polymer
will be excellent in solubility.
As preferred fluorinated solvents (2), the following may be
exemplified.
F(CF.sub.2).sub.4OCH.sub.3, CF.sub.3CH.sub.2OCF.sub.2CF.sub.2H,
F(CF.sub.2).sub.5OCH.sub.3, F(CF.sub.2).sub.6OCH.sub.3,
F(CF.sub.2).sub.7OCH.sub.3, F(CF.sub.2).sub.8OCH.sub.3,
F(CF.sub.2).sub.9OCH.sub.3, F(CF.sub.2).sub.10OCH.sub.3,
H(CF.sub.2).sub.6OCH.sub.3,
(CF.sub.3).sub.2CFCF(OCH.sub.3)CF.sub.2CF.sub.3,
F(CF.sub.2).sub.3OCF(CF.sub.3)CF.sub.2OCH.sub.3,
F(CF.sub.2).sub.3OCF(CF.sub.3)CF.sub.2OCF(CF.sub.3)CF.sub.2OCH.sub.3,
F(CF.sub.2).sub.8OCH.sub.2CH.sub.2CH.sub.3,
(CF.sub.3).sub.2CFCF.sub.2CF.sub.2OCH.sub.3,
F(CF.sub.2).sub.2O(CF.sub.2).sub.4OCH.sub.2CH.sub.3.
Among such fluorinated solvents, particularly preferred is
(CF.sub.3).sub.2CFCF(OCH.sub.3)CF.sub.2CF.sub.3.
To the above coating composition, a silane coupling agent may be
incorporated, whereby a coating film formed by using such a
fluoropolymer composition is excellent in the adhesion to the
substrate.
The silane coupling agent is not particularly limited, and a wide
range of silane coupling agents including known agents may be used.
The following ones may specifically be exemplified.
A monoalkoxysilane such as trimethylmethoxysilane,
trimethylethoxysilane, dimethylvinylmethoxysilane or
dimethylvinylethoxysilane.
A dialkoxysilane such as .gamma.-chloropropylmethyldimethoxysilane,
.gamma.-chloropropylmethyldimethoxysilane,
.gamma.-aminopropylmethyldiethoxysilane,
.gamma.-aminopropylmethyldimethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropylmethyldimethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropylmethyldiethoxysilane,
.gamma.-glycidyloxypropylmethyldimethoxysilane,
.gamma.-glycidyloxypropylmethyldiethoxysilane,
.gamma.-methacryloyloxypropylmethyldimethoxysilane,
methyldimethoxysilane, methyldiethoxysilane,
dimethyldimethoxysilane, dimethyldiethoxysilane,
methylvinyldimethoxysilane, methylvinyldiethoxysilane,
diphenyldimethoxysilane, diphenyldiethoxysilane,
3,3,3-trifluoropropylmethyldimethoxysilane,
3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctylmethyldimethoxysilane
or
3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecylmethyldimethoxys-
ilane.
A tri- or tetra-alkoxysilane such as
.gamma.-aminopropyltrimethoxysilane,
.gamma.-aminopropyltriethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropyltriethoxysilane,
.gamma.-mercaptopropyltrimethoxysilane,
.gamma.-glycidyloxypropyltrimethoxysilane,
.gamma.-glycidyloxypropyltriethoxysilane,
.gamma.-methacryloyloxypropyltrimethoxysilane,
.gamma.-chloropropyltrimethoxysilane, methyltriethoxysilane,
phenyltrimethoxysilane, phenyltriethoxysilane,
3,3,3-trifluoropropyltrimethoxysilane,
3,3,4,4,5,5,6,6,7,7,8,8,8-tridecafluorooctyltrimethoxysilane,
3,3,4,4,5,5,6,6,7,7,8,8,9,9,10,10,10-heptadecafluorodecyltrimethoxysilane-
, tetramethoxysilane or tetraethoxysilane.
Further, as a preferred silane coupling agent, an aromatic amine
type silane coupling agent being a silane coupling agent having an
aromatic amine structure may be mentioned. Compounds represented by
the following formulae (s1) to (s3) may be mentioned as such
aromatic amine type silane coupling agents.
ArSi(OR.sup.21)(OR.sup.22)(OR.sup.23) (s1)
ArSiR.sup.24(OR.sup.21)(OR.sup.22) (s2)
ArSiR.sup.24R.sup.25(OR.sup.21) (s3) wherein each of R.sup.21 to
R.sup.25 which are independent of one another, is a hydrogen atom,
a C.sub.1-20 alkyl group or an aryl group, and Ar is a p-, m- or
o-aminophenyl group.
As specific examples of the compounds represented by the formulae
(s1) to (s3), the following ones may be mentioned.
Aminophenyltrimethoxysilane, aminophenyltriethoxysilane,
aminophenyltripropoxysilane, aminophenyltriisopropoxysilane,
aminophenylmethyldimethoxysilane, aminophenylmethyldiethoxysilane,
aminophenylmethyldipropoxysilane,
aminophenylmethyldiisopropoxysilane,
aminophenylphenyldimethoxysilane, aminophenylphenyldiethoxysilane,
aminophenylphenyldipropoxysilane, aminophenyldiisopropoxysilane,
etc.
A hydrogen atom of an amino group in these compounds may be
substituted by an alkyl group or an aryl group. For example,
N,N-dimethylaminophenyltrialkoxysilane or
N,N-dimethylaminophenylmethyldialkoxysilane may, for example, be
mentioned. In addition, for example, aromatic amine type silane
coupling agents disclosed in U.S. Pat. No. 3,481,815 may be
used.
The above silane coupling agents may be used alone, or two or more
of them may be used in combination.
Further, a partially hydrolyzed condensate of the above silane
coupling agent may preferably be used.
Further, a co-partially hydrolyzed condensate of the above silane
coupling agent with a tetraalkoxysilane such as tetramethoxysilane,
tetraethoxysilane or tetrapropoxysilane, may also preferably be
used. Among them, as one to improve the adhesion of the polymer
compound (a) without impairing the electrical insulation properties
of the polymer compound (a), a silane coupling agent having an
amino group (such as .gamma.-aminopropyltriethoxysilane,
.gamma.-aminoproplymethyldiethoxysilane,
.gamma.-aminopropyltrimethoxysilane,
.gamma.-aminopropylmethyldimethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropyltrimethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropylmethyldimethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropyltriethoxysilane,
N-(.beta.-aminoethyl)-.gamma.-aminopropylmethyldiethoxysilane,
aminophenyltrimethoxysilane, aminophenyltriethoxysilane,
aminophenylmethyldimethoxysilane or
aminophenylmethyldiethoxysilane) or a silane coupling agent having
an epoxy group (such as .gamma.-glycidyloxypropyltrimethoxysilane,
.gamma.-glycidyloxypropylmethyldimethoxysilane,
.gamma.-glycidyloxypropyltriethoxysilane or
.gamma.-glycidyloxypropylmethyldiethoxysilane) may be exemplified
as a particularly preferred one.
In a case where as the polymer compound (a), one having a carboxy
group preliminarily introduced to a side chain or at a terminal of
the main chain, is used, an alkoxysilane having an amino group or
an epoxy group is particularly effective as the silane coupling
agent.
In a case where as the polymer compound (a), one having an alkoxy
carbonyl group preliminarily introduced to a side chain or at a
terminal of the main chain is used, an alkoxysilane having an amino
group or an aminophenyl group is particularly effective as a silane
coupling agent.
In a case where as a coating composition, an aprotic fluorinated
solvent solution of a fluororesin is used, a protic fluorinated
solvent may be incorporated to such a coating composition. When a
protic fluorinated solvent is incorporated to the coating
composition, it is possible to increase the solubility of the
silane coupling agent in the coating composition. Further, it is
possible to suppress an increase of the viscosity or gelation which
is considered to be attributable to a reaction of the silane
coupling agent itself.
That is, in an aprotic fluorinated solvent, the above-mentioned
trialkoxysilane having an amino group or an epoxy group is likely
to undergo gelation or viscosity increase with time, as compared
with a dialkoxysilane having a similar group. Further, a
trialkoxysilane has a smaller solubility in an aprotic fluorinated
solvent solution of the coating composition, than the
dialkoxysilane. Accordingly, in a case where as the coating
composition, an aprotic fluorinated solvent solution is used, and a
trialkoxysilane is incorporated thereto, it is preferred to further
add a protic fluorinated solvent, particularly a fluorinated
alcohol.
In a case where a dialkoxysilane is incorporated as a coupling
agent, although the solubility is not so small as a
trialkoxysilane, it is possible to improve the solubility by
likewise adding a protic fluorinated solvent, particularly a
fluorinated alcohol. In the case of the dialkoxysilane, the
viscosity increase with time of the coating composition is not so
remarkable as the trialkoxysilane, and accordingly, it is not
necessarily required to add a protic fluorinated solvent such as a
fluorinated alcohol. However, it is preferred to add such a protic
fluorinated solvent, whereby the viscosity increase can certainly
be suppressed.
As such a protic fluorinated solvent, the following ones may be
exemplified.
A fluorinated alcohol such as trifluoroethanol,
2,2,3,3,3-pentafluoro-1-propanol, 2-(perfluorobutyl)ethanol,
2-(perfluorohexyl)ethanol, 2-(perfluorooctyl)ethanol,
2-(perfluorodecyl)ethanol, 2-(perfluoro-3-methylbutyl)ethanol,
2,2,3,3-tetrafluoro-1-propanol,
2,2,3,3,4,4,5,5-octafluoro-1-pentanol,
2,2,3,3,4,4,5,5,6,6,-dodecafluoro-1-heptanol,
2,2,3,3,4,4,5,5,6,6,7,7-hexadecafluoro-1-nonanol,
1,1,1,3,3,3-hexafluoro-2-propanol or
2,2,3,3,4,4-hexafluoro-1-butanol.
A fluorinated carboxylic acid such as trifluoroacetic acid,
perfluoropropanoic acid, perfluorobutanoic acid, perfluoropentanoic
acid, perfluorohexanoic acid, perfluoroheptanoic acid,
perfluorooctanoic acid, perfluorononanoic acid, perfluorodecanoic
acid, 1,1,2,2-tetrafluoropropanoic acid,
1,1,2,2,3,3,4,4-octafluoropentanoic acid,
1,1,2,2,3,3,4,4,5,5-dodecafluoroheptanoic acid or
1,1,2,2,3,3,4,4,5,5,6,6-hexadecafluorononanoic acid, amides of
these fluorinated carboxylic acids, or a fluorinated sulfonic acid
such as trifluoromethanesulfonic acid or
heptadecafluorooctanesulfonic acid.
These protic fluorinated solvents may be used alone, or two or more
of them may be used in combination.
In a case where an aprotic fluorinated solvent and a protic
fluorinated solvent are used in combination, the proportion of the
protic fluorinated solvent based on the sum of the aprotic
fluorinated solvent and the protic fluorinated solvent is
preferably from 0.01 to 50 mass %, more preferably from 0.1 to 30
mass %.
The concentration of the polymer compound (a) in the coating
composition may suitably be set depending upon the thickness of the
layer (A) to be formed. It is usually from 0.1 to 30 mass %,
preferably from 0.5 to 20 mass %.
Further, in a case where a silane coupling agent is incorporated to
the coating composition, the amount is preferably from 0.01 to 50
parts by mass, more preferably from 0.1 to 30 parts by mass, per
100 parts by mass of the polymer compound (a).
<Layer (B)>
The layer (B) is a layer constituted by a polymer compound (b) or
an inorganic substance (c), and the difference in the relative
dielectric constant between the material constituting the layer (B)
(the polymer compound (b) or the inorganic substance (c)) and the
material constituting the layer (A) (the polymer compound (a)) is
at least 0.3. The larger the difference in the relative dielectric
constant, the better the effect to increase the surface charge
density. Therefore, the difference in the relative dielectric
constant is preferably at least 0.5, more preferably at least
0.8.
The upper limit of the difference in the relative dielectric
constant is not particularly limited, but from the viewpoint of
availability of the materials, efficiency for forming the laminate
structure, etc., it is preferably 5.5, more preferably 4.0, further
preferably 2.0.
The polymer compound (b) may be any so long as its relative
dielectric constant is higher by at least 0.3 than the relative
dielectric constant of the polymer compound (a), and it may
suitably be selected from known polymer compounds taking into
consideration the relative dielectric constant of the polymer
compound (a) to be used for the layer (A), the above-described
desired value of the difference in the relative dielectric
constant, etc.
The relative dielectric constant of the polymer compound (b) may
vary also depending upon the relative dielectric constant of the
polymer compound (a), but is preferably from 2.5 to 8.0, more
preferably from 2.5 to 5.0. When the relative dielectric constant
is at least the lower limit within the above range, the surface
charge density as an electret characteristic will be high, and when
it is at most the upper limit, the charge retention stability as an
electret will be excellent.
Specifically, the polymer compound (b) is preferably at least one
member selected from the group consisting of a fluororesin, a
polyimide, a polyparaxylylene resin, a polycarbonate, a
polyarylene, a polyarylene ether, a polyether, a polyether sulfone,
a polyether ketone, a polyether nitrile, a polyether imide, a
polythioether sulfone, a polysulfone, nylon, a polyester, a
polystyrene, a polyethylene, a polypropylene, a polyketone, an
epoxy resin, an acrylic resin, a polyurethane, an aramid resin and
a cycloolefin polymer. Among them, from the viewpoint of the
relative dielectric constant, at least one member selected from the
group consisting of a polyimide, a polyparaxylylene resin, a
polycarbonate, a polyarylene, a polyarylene ether, a polysulfone
and a polyether sulfone is preferred. Among them, as the
fluororesin and the cycloolefin polymer, the same ones as the
fluororesin and the cycloolefin polymer mentioned as examples for
the above polymer compound (a) may, respectively, be exemplified.
However, in a case where the fluororesin or the cycloolefin polymer
is used as the polymer compound (b), one having a relative
dielectric constant higher by at least 0.3 than the polymer
compound (a) is used as such a fluororesin or a cycloolefin
polymer.
Further, as a preferred fluororesin, the following "fluorinated
aromatic resin containing a fluorinated aromatic polymer as the
main component" may be mentioned.
The "fluorinated aromatic resin" is a resin containing a
fluorinated aromatic polymer as the main component. The
"fluorinated aromatic polymer" is a polymer having fluorine atoms
and an aromatic ring in its molecule (a fluorinated polymer having
an aromatic ring). The polymer being the main component of the
resin means that the polymer occupies at least 50 mass % in the
resin.
In the present invention, the proportion of the fluorinated
aromatic polymer in the fluorinated aromatic resin is preferably at
least 80 mass % and may be 100 mass %.
The fluorinated aromatic polymer contained in the fluorinated
aromatic resin may be one type, or two or more types.
In this specification, the "aromatic ring" means a cyclic structure
in a cyclic organic compound having an aromatic nature, and unless
otherwise specified, it includes one having an optional
substituent.
The aromatic ring which the fluorinated aromatic polymer has, may
be a hydrocarbon ring comprising carbon atoms and hydrogen atoms,
or a heterocyclic ring containing a heteroatom such as a nitrogen
atom, an oxygen atom or a sulfur atom, or may be a mixture
thereof.
The hydrocarbon ring may, for example, be benzene, naphthalene,
anthracene, phenanthrene, tetracene or pentacene.
The hetero ring may, for example, be pyrrole, furan, thiophene,
imidazole, oxazole, thiazole, pyrazole, isooxazole, isothiazole,
pyridine, pyridazine, pyrimidine or pyrazine.
In the fluorinated aromatic polymer, a plurality of aromatic rings
are preferably linked by a linking group. Here, the linking group
may, for example, be a single bond, an alkylene group, an etheric
oxygen atom (--O--), or an atomic group of e.g. sulfide, sulfone,
carbonyl, ester or amide.
In the present invention, the fluorinated aromatic polymer
preferably has a molecular structure in which fluorine atoms are
directly bonded to an aromatic ring. That is, it preferably has an
aromatic ring having fluorine atoms directly bonded (a fluorine
atom-substituted aromatic ring) in its molecular structure.
In such a case, in the fluorinated aromatic polymer, fluorine atoms
not bonded to the aromatic ring (bonded to chain-form carbon) may
be present.
Further, in the fluorine atom-substituted aromatic ring, fluorine
atoms may be bonded or may not be bonded to all carbon atoms
constituting the fluorine atom-substituted aromatic ring. Further,
fluorine atoms may be bonded or may not be bonded to all aromatic
rings present in the fluorinated aromatic polymer.
As specific examples of the fluorinated aromatic polymer, a
fluorinated aromatic polyimide, a fluorinated polybenzooxazole, a
fluorinated polybenzoimidazole, a fluorinated polyphenylene
sulfide, a fluorinated aromatic polysulfone, a fluorinated aromatic
polyether sulfone, a fluorinated aromatic polyester, a fluorinated
aromatic polycarbonate, a fluorinated aromatic polyamide imide, a
fluorinated aromatic polyamide, a fluorinated aromatic polyether
imide, a fluorinated polyarylene, a fluorinated polyphenylene
oxide, a fluorinated aromatic polyether ether ketone and a
fluorinated polyarylene ether may, for example, be exemplified.
Among them, a fluorinated aromatic polyimide, a fluorinated
polybenzooxazole, a fluorinated aromatic polyether sulfone, a
fluorinated aromatic polyether imide, a fluorinated polyarylene, a
fluorinated aromatic polyether ether ketone and a fluorinated
polyarylene ether are, for example, preferred since they have low
relative dielectric constants and low moisture absorption and are
excellent in electret properties.
Further, among the above, the fluorinated aromatic polymer is more
preferably a fluorinated polyarylene and/or a fluorinated
polyarylene ether. Particularly preferred is one wherein the main
chain has a branched structure, since such a polymer is excellent
in heat resistance.
In the present invention, the fluorinated polyarylene means a
polyarylene having at least one fluorine atom in its structure, and
the "polyarylene" means a polymer having a polyarylene structure in
the main chain.
The "polyarylene structure" means a polymer structure wherein a
structure having one or more aromatic rings is repeated, and
"having a polyarylene structure in the main chain" means that in
each aromatic ring constituting the polyarylene structure, at least
two carbon atoms constituting the aromatic ring are carbon atoms in
the carbon chain constituting the main chain.
In this specification, among carbon chains constituting the
fluorinated polyarylene, a portion containing a polyarylene
structure, or a portion containing "an aromatic ring wherein at
least two carbon atoms are carbon atoms in the carbon chain" is
regarded as a part of the main chain, and a terminal portion
containing no such a structure is referred to as "a side
chain".
The carbon chain constituting the main chain of the fluorinated
polyarylene may be linear or branched. It is preferably branched
from the viewpoint of the effects of the present invention.
The fluorinated polyarylene preferably has fluorine atoms which are
directly bonded to an aromatic ring. That is, the fluorinated
polyarylene preferably has a fluorine atom-substituted aromatic
ring.
As such a fluorinated polyarylene, a polymer having a fluorinated
aryl structural unit having one or more aromatic rings to which one
or more fluorine atoms are bonded, may, for example, be preferably
exemplified, since it has low moisture absorption and is excellent
in the characteristics of the obtainable electret.
As such fluorinated aryl structural units, structural units
represented by the following formulae (b1) to (b6) may, for
example, be mentioned.
##STR00013##
In this specification, F in an aromatic ring in each formula
represents that all hydrogen atoms in the aromatic ring are
substituted by fluorine atoms.
In such a fluorinated aryl structural unit, some of fluorine atoms
bonded to the aromatic ring may be substituted by other atoms or
substituents. Other atoms may, for example, be hydrogen atoms. The
substituents may, for example, be C.sub.1-8 fluorinated alkyl
groups.
The fluorinated polyarylene may be one having one type of
fluorinated aryl structural units, or one having two or more types
of fluorinated aryl structural units.
The fluorinated polyarylene having one type of fluorinated aryl
structural units may, for example, be a fluorinated polyphenylene,
a fluorinated polybiphenylene or a fluorinated
polynaphthanylene.
The fluorinated polyarylene having two or more fluorinated aryl
structural units may, for example, be a polyarylene represented by
the following formula (B1) (hereinafter referred to as a
fluorinated polyarylene (B1)).
##STR00014## wherein each of m and n which are independent of each
other, is an integer of from 0 to 4, and 1.ltoreq.m+n.ltoreq.5;
each of p, q and r which are independent of one another, is an
integer of from 0 to 5; and each of a, b and c which are
independent of one another, is an integer of from 0 to 3.
When m+n is at least 2, the fluorinated polyarylene (B1) will be
one having the main chain of a branched structure, and as mentioned
above, is preferred, since it is excellent in heat resistance.
Accordingly, m+n is preferably an integer of from 2 to 5, more
preferably 2 or 3.
Each of p, q and r which are independent of one another, is
preferably an integer of from 0 to 3.
Each of a, b and c which are independent of one another, is
preferably an integer of from 0 to 2.
As specific examples of the fluorinated polyarylene (B1),
polyarylenes represented by the following formulae (B1-1) to (B1-4)
may be mentioned.
##STR00015## ##STR00016## wherein a1, b1 and c1 are, respectively,
the same as the above-mentioned a, b and c.
The number average molecular weight of the fluorinated polyarylene
is preferably at a level of from 400 to 10,000, and from the
viewpoint of the film forming property, it is more preferably at a
level of from 1,000 to 5,000.
In the present invention, the fluorinated polyarylene ether means a
polyarylene ether having at least one fluorine atom in its
structure, and the "polyarylene ether" means a polymer having a
polyarylene ether structure in the main chain.
The "polyarylene ether structure" means a polymer structure wherein
a structure having two aromatic rings linked by an ether bond
(--O--) is repeated, and "having a polyarylene ether structure in
the main chain" means that in each aromatic ring constituting the
polyarylene ether structure, at least two carbon atoms constituting
the aromatic ring are carbon atoms in the carbon chain constituting
the main chain (provided that an ether bond linking the aromatic
rings is regarded as a part of the carbon chain constituting the
main chain).
In this specification, among carbon chains constituting the
fluorinated polyarylene ether, a portion containing a polyarylene
ether structure, or a portion containing "an aromatic ring wherein
at least two carbon atoms are carbon atoms in the carbon chain" is
regarded as a part of the main chain, and a terminal portion
containing no such a structure is referred to as "a side
chain".
The carbon chain constituting the main chain of the fluorinated
polyarylene ether may be linear or branched. It is preferably
branched from the viewpoint of the effects of the present
invention.
The fluorinated polyarylene ether preferably has fluorine atoms
which are directly bonded to an aromatic ring. That is, the
fluorinated polyarylene ether preferably has a fluorine
atom-substituted aromatic ring.
Such a fluorinated polyarylene ether is preferably a polymer having
a poly-substituted phenylene ether structural unit which has one or
more aromatic rings and wherein at least three oxygen atoms are
directly bonded to optional one or more aromatic rings, and a
fluorinated aryl ether structural unit which has one or more
aromatic rings to which one or more fluorine atoms are bonded and
wherein the aromatic rings to which fluorine atoms are bonded, are
bonded to the above oxygen atoms, since the polymer has low
moisture absorption and is excellent in the characteristics of the
obtainable electret.
The poly-substituted phenylene ether structural unit may, for
example, be a structural unit derived from trihydroxybenzene, or a
structural unit derived from trisphenol.
The fluorinated aryl ether structural unit may, for example, be one
wherein an oxygen atom (--O--) is bonded to e.g. an aromatic ring
of the above-mentioned fluorinated aryl structural unit.
As the polymer having the poly-substituted phenylene ether
structural unit and the fluorinated aryl ether structural unit, a
fluorinated aromatic polymer disclosed in e.g. JP-A-10-74750,
WO03/8483, JP-A-2005-105115, etc. may, for example, be
exemplified.
As the fluorinated aromatic polymer, particularly preferred is a
cured product which is formed by curing a crosslinkable fluorinated
aromatic prepolymer (hereinafter sometimes referred to as a
crosslinkable fluorinated aromatic prepolymer (B2)). When the
fluorinated aromatic polymer (B2) is such a cured product, the
electret will be excellent in e.g. durability. That is, the
crosslinkable fluorinated aromatic prepolymer (B2) is soluble in a
solvent to obtain a solution, and by using such a solution, the
layer (B) can be formed as a coating film. Such a coating film will
be excellent in durability against high temperature treatment, and,
for example, as compared with a case wherein a resin film such as
PTFE is bonded to a substrate or a layer (A), a problem such as
peeling or deformation is less likely to occur. Therefore, at the
time of producing an electret, injection of electric charge can be
carried out at a relatively high temperature (e.g. from 100 to
180.degree. C.). Electric charge injected at such a high
temperature is excellent in stability, and the durability as an
electret will be excellent.
The crosslinkable fluorinated aromatic prepolymer (B2) is a
fluorinated aromatic polymer having a crosslinkable functional
group.
The crosslinkable functional group is a reactive functional group
which is substantially free from a reaction during the production
of the prepolymer and which undergoes a reaction to cause
crosslinking among prepolymer molecules or extension of the chain,
when an external energy is exerted at the time of preparing a cured
product or at an optional time after the preparation of a cured
product. The external energy may, for example, be heat, light,
electron beams, etc., or a combination thereof.
In a case where heat is used as the external energy, a
crosslinkable functional group is preferred which undergoes a
reaction at a temperature of from 40 to 500.degree. C. If the
temperature for the reaction is too low, the stability cannot be
secured during the storage of the prepolymer, and if it is too
high, thermal decomposition of the prepolymer itself is likely to
take place. Therefore, the temperature is preferably within the
above range, more preferably from 60 to 400.degree. C., most
preferably from 70 to 350.degree. C.
In a case where light is used as the external energy, it is also
preferred to further add a photo-radical-generating agent, a
photo-acid-generating agent, a sensitizer, etc. depending upon
light with a specific wavelength. As the crosslinkable functional
group, a crosslinkable functional group containing no polar group
is preferred not to increase the relative dielectric constant of
the cured product. Such a polar group, may, for example, be a
hydroxy group, an amino group, a carbonyl group or a cyano
group.
As specific examples of the crosslinkable functional group, a vinyl
group, an allyl group, a methacryloyl(oxy) group, an acryloyl(oxy)
group, a vinyloxy group, a trifluorovinyl group, a
trifluorovinyloxy group, an ethynyl group, a
1-oxocyclopenta-2,5-diene-3-yl group, a cyano group, an alkoxy
silyl group, a diaryl hydroxymethyl group and a hydroxyfluorenyl
group may, for example, be mentioned. Among them, a vinyl group, a
methacryloyl(oxy) group, an acryloyl(oxy) group, a
trifluorovinyloxy group or an ethynyl group is preferred, since the
reactivity is thereby high, and a high crosslinking density can be
obtained. Further, an ethynyl group or a vinyl group is preferred
from such a viewpoint that the obtainable cured product will have
good heat resistance.
The crosslinkable functional group may be present in the main chain
or in a side chain of the crosslinkable fluorinated aromatic
prepolymer (B2). Here, "the crosslinkable functional group is
present in the main chain" means that at least one carbon atom
constituting the crosslinkable functional group (which may contain
an ether bond) is the carbon atom in the carbon chain constituting
the main chain.
From the viewpoint of availability of raw materials, it is
preferred that the crosslinkable functional group is present in a
side chain, and no crosslinkable functional group is present in the
main chain.
The crosslinkable functional group may be introduced, for example,
by using a compound having a crosslinkable functional group, as a
material for the prepolymer (e.g. the after-mentioned compound
(Y-1), compound (Y-2), etc.).
In the present invention, the crosslinkable fluorinated aromatic
prepolymer (B2) is obtained by subjecting either one or both of a
compound (Y-1) having a crosslinkable functional group and a
phenolic hydroxyl group and a compound (Y-2) having a crosslinkable
functional group and a fluorine atom-substituted aromatic ring to a
condensation reaction with a fluorinated aromatic compound (Z)
represented by the following formula (Z) and a compound (C) having
at least 3 phenolic hydroxyl groups, in the presence of a HF
(hydrogen fluoride)-removing agent. The crosslinkable fluorinated
aromatic prepolymer (B2) is preferably a fluorinated polyarylene
ether which has a crosslinkable functional group and an ether bond
and which has a number average molecular weight of from
1.times.10.sup.3 to 1.times.10.sup.5.
##STR00017## wherein s is an integer of from 0 to 3, each of t and
u which are independent of each other is an integer of from 0 to 3,
each of Rf.sup.1 and Rf.sup.2 which are independent of each other,
is a C.sub.1-8 fluorinated alkyl group, provided that in a case
where a plurality of Rf.sup.1 or Rf.sup.2 are present, the
plurality of Rf.sup.1 or Rf.sup.2 may be the same or different from
one another.
A cured product of the above fluorinated polyarylene ether
(hereinafter sometimes referred to as the prepolymer (B2-1)) is a
fluorinated polyarylene ether. Such a cured product is produced by
using the compound (C) having at least three phenolic hydroxyl
groups and it further has crosslinkable functional groups, whereby
it satisfies the high heat resistance and excellent stability of
the electret characteristics at the same time. That is, as the
prepolymer (B2-1) has crosslinkable functional groups, crosslinking
among the prepolymer (B2-1) molecules or the chain-extending
reaction can be promoted, whereby the heat resistance of the
obtainable cured product will be substantially improved, and at the
same time, the solvent resistance will be improved.
Further, by using the above-mentioned fluorinated aromatic compound
(Z), the flexibility of the obtainable cured product will be good.
That is, as compared with a fluorinated aromatic prepolymer
produced by using a fluorinated aromatic compound which by itself
has a branched structure, the density of ether bonds can be
increased, and the flexibility of the main chain will be improved,
and as a result, the flexibility of the obtainable cured product
will be good, and further, the flexibility of the electret will be
good.
As the crosslinkable functional group which the compound (Y-1) and
the compound (Y-2) have, the same one as the crosslinkable
functional group mentioned in the description of the crosslinkable
fluorinated aromatic prepolymer may be mentioned.
The compound (Y-1) has a crosslinkable functional group and a
phenolic hydroxy group.
As the compound (Y-1), a compound (Y-1-1) having a crosslinkable
functional group and one phenolic hydroxy group, and/or a compound
(Y-1-2) having a crosslinkable functional group and two phenolic
hydroxy groups, is preferred. As specific examples of the compound
(Y-1-1), a phenol having a reactive double bond such as
4-hydroxystyrene and an ethynyl phenol such as 3-ethynyl phenol,
4-phenyl ethynyl phenol or 4-(4-fluorophenyl)ethynyl phenol may be
mentioned. They may be used alone or in combination as a mixture of
two or more of them.
As specific examples of the compound (Y-1-2), a
bis(phenylethynyl)dihydroxybiphenyl such as
2,2'-bis(phenylethynyl)-5,5'-dihydroxybiphenyl or
2,2'-bis(phenylethynyl)-4,4'-dihydroxybiphenyl, and a
dihydroxydiphenyl acetylene such as 4,4'-dihydroxytolan or
3,3'-dihydroxytolan, may be mentioned. They may be used alone or in
combination as a mixture of two or more of them.
In the present invention, as the compound (Y-1), one wherein the
hydrogen atom of its phenolic hydroxy group is substituted by a
protective group such as an acetyl group, a pivaloyl group or a
benzoyl group, may be used. In such a compound, the protective
group may be dissociated by an alkali (HF removing agent) such as
potassium hydroxide to be used for the condensation reaction,
whereby a phenolic hydroxy group will be formed. As such a
compound, 4-acetoxy styrene may, for example, be mentioned.
The compound (Y-2) has a crosslinkable functional group and a
fluorine atom-substituted aromatic ring.
As the compound (Y-2), preferred is a compound having a
crosslinkable functional group and a perfluoro aromatic ring such
as perfluorophenyl or perfluorobiphenyl. As its specific examples,
a fluorinated aryl having a reactive double bond, such as
pentafluorostyrene, pentafluorobenzyl acrylate, pentafluorobenzyl
methacrylate, pentafluorophenyl acrylate, pentafluorophenyl
methacrylate, perfluorostyrene, pentafluorophenyltrifluorovinyl
ether or 3-(pentafluorophenyl)pentafluoropropene, a fluorinated
aryl having a cyano group, such as pentafluorobenzonitrile; a
fluorinated arylacetylene such as pentafluorophenylacetylene or
nonafluorobiphenylacetylene; and a fluorinated diarylacetylene such
as phenylethynylpentafluorobenzene, phenylethynylnonafluorobiphenyl
or decafluorotolan, may, for example, be mentioned. They may be
used alone or in combination as a mixture of two or more of
them.
As the compound (Y-2), a fluorinated arylacetylene is preferred,
since the crosslinking reaction thereby proceeds at a relatively
low temperature, and the heat resistance of the obtainable cured
product will be improved.
The fluorinated aromatic compound (Z) is represented by the above
formula (Z).
In the formula (Z), s is most preferably 1.
The fluorinated alkyl group for Rf.sup.1 and Rf.sup.2 is preferably
a perfluoroalkyl group from the viewpoint of the heat resistance.
As specific examples, a perfluoromethyl group, a perfluoroethyl
group, a perfluoropropyl group, a perfluorobutyl group, a
perfluorohexyl group and a perfluorooctyl group may be
mentioned.
Each of t and u which are independent of each other, is preferably
an integer of from 0 to 2, most preferably 0. The smaller the value
of t and u, i.e. the smaller the number of Rf.sup.1 and Rf.sup.2,
the easier the production of the fluorinated aromatic compound
(Z).
As specific examples of the fluorinated aromatic compound (Z), in a
case where is 0, perfluorobenzene, perfluorotoluene,
perfluoroxylene, etc. may be mentioned. In a case where s is 1,
perfluorobiphenyl, etc. may be mentioned. In a case where s is 2,
perfluoroterphenyl, etc. may be mentioned. In a case where s is 3,
perfluoro(1,3,5-triphenylbenzene) or
perfluoro(1,2,4-triphenylbenzene) is preferred, and
perfluorobenzene or perfluorobiphenyl is particularly preferred.
They may be used alone or in combination as a mixture of two or
more of them.
In the compound (C) having at least three phenolic hydroxy groups,
the number of phenolic hydroxy groups may be at least 3,
practically preferably from 3 to 6, particularly preferably from 3
to 4.
As the compound (C), a poly-functional phenol is preferred. As
specific examples, trihydroxybenzene, trihydroxybiphenyl,
trihydroxynaphthalene, 1,1,1-tris(4-hydroxyphenyl)ethane,
tris(4-hydroxyphenyl)benzene, tetrahydroxybenzene,
tetrahydroxybiphenyl, tetrahydroxybinaphthyl, a
tetrahydroxyspiroindan, etc. may be mentioned.
As the compound (C), a compound having three phenolic hydroxy
groups is preferred, since the flexibility of the cured film
thereby obtainable will be high. Among them, trihydroxybenzene or
1,1,1-tris(4-hydroxyphenyl)ethane is particularly preferred, since
the dielectric constant of the obtainable cured product will be
low.
As the HF-removing agent to be used for the above condensation
reaction, a basic compound is preferred, and particularly preferred
is a carbonate, hydrogen carbonate or hydroxide of an alkali metal.
As specific examples, sodium carbonate, potassium carbonate, sodium
hydrogencarbonate, potassium hydrogencarbonate, sodium hydroxide or
potassium hydroxide, may, for example, be mentioned.
The prepolymer (B2-1) has crosslinkable functional groups derived
from the compound (Y-1) and/or the compound (Y-2).
The content of crosslinkable functional groups in the prepolymer
(B2-1) is preferably from 0.1 to 4 mmol, more preferably from 0.2
to 3 mmol, of the crosslinkable functional groups, per 1 g of the
prepolymer (B2-1). By adjusting this content to be at least 0.1
mmol, the heat resistance and solvent resistance of the cured
product can be made high, and by adjusting it to be at most 4 mmol,
brittleness can easily be controlled to be small.
The prepolymer (B2-1) may have a side chain represented by the
following formula (I) in addition to a crosslinkable functional
group and an ether bond. When the prepolymer (B2-1) has such a side
chain, the cured product will be excellent in flexibility or
elasticity. Rf--CH.sub.2--O-- (I) wherein Rf represents a
C.sub.3-50 fluorinated alkyl group (provided that it may contain an
etheric oxygen atom).
In the above formula (I), Rf represents a C.sub.3-50 fluorinated
alkyl group, which may contain an etheric oxygen atom. The
fluorinated alkyl group as Rf means one wherein some or all of
hydrogen atoms bonded to carbon atoms of an alkyl group are
substituted by fluorine atoms. Further, such a fluorinated alkyl
group may be a chain-form alkyl group or a cycloalkyl group.
Rf is preferably linear, branched or cyclic. Further, Rf is
preferably a perfluoroalkyl group wherein all of hydrogen atoms
bonded to carbon atoms of an alkyl group are substituted by
fluorine atoms.
As a linear one among side chains represented by the above formula
(I), one represented by the following formula (I-1) or (I-2) is
preferred. As a more preferred example of the side chain
represented by the following formula (I-1), a monovalent group
represented by the following formula (I-1-1) or (I-1-2) may be
mentioned. Rf.sup.a-O--(CF.sub.2).sub.m--CH.sub.2--O-- (I-1)
CF.sub.3(OCF.sub.2CF.sub.2).sub.k--O--CF.sub.2--CH.sub.2--O--
(I-1-1)
C.sub.pF.sub.2p+1OCF.sub.2CF.sub.2--O--CF.sub.2--CH.sub.2--O--
(I-1-2) CF.sub.3(CF.sub.2).sub.j--CH.sub.2--O-- (I-2)
In the formula (I-1), m is an integer of from 1 to 5, and Rf.sup.a
is a C.sub.4-50 fluorinated alkyl group, which may contain an
etheric oxygen atom. It is more preferred that m is an integer of
from 1 to 3.
In the formula (I-1-1), k is an integer of from 1 to 10.
In the formula (I-1-2), p is an integer of from 1 to 10.
In the formula (I-2), j is an integer of from 2 to 40.
As a branched chain type among side chains represented by the above
formula (I), a monovalent group represented by the following
formula (I-3) or (I-4) is preferred.
CF.sub.3C.sub.2F.sub.4O[CF(CF.sub.3)CF.sub.2O].sub.iCF(CF.sub.3)--CH.sub.-
2--O-- (I-3)
F[CF.sub.2CF(CF.sub.3)C.sub.2F.sub.4O].sub.hCF.sub.2CF(CF.sub.3)CF.sub.2--
-CH.sub.2--O--(I-4)
In the formula (I-3), i is an integer of from 0 to 10.
In the formula (I-4), h is an integer of from 0 to 10.
A cyclic type among side chains represented by the above formula
(I), a monovalent group represented by the following formula (I-5),
(I-6) or (I-7) is preferred.
##STR00018##
The position at which the side chain represented by the formula (I)
is introduced, is not particularly limited, but from the viewpoint
of the production, it is preferred that such a side chain is bonded
to a halogen-substituted aromatic ring in the main chain. That is,
it is preferred that a halogen-substituted aromatic ring is present
in the main chain, and a side chain represented by the formula (I)
is bonded to such an aromatic ring.
The halogen-substituted aromatic ring to which the side chain is
bonded, may be an aromatic ring constituting a polyarylene ether
structure or may be another aromatic ring other than that. From
such a viewpoint that the production of a prepolymer is easy, the
latter is more preferred, i.e. a side chain represented by the
formula (I) is bonded to a halogen-substituted aromatic ring not
constituting a polyarylene ether structure. Further, the
halogen-substituted aromatic ring to which such a side chain is
bonded, is more preferably a perfluoroaromatic ring.
"The side chain represented by the formula (I)" present in one
molecule of the prepolymer (B2-1) may be one type, or two or more
types. The content of "the side chain represented by the formula
(I)" in the prepolymer (B2-1) is preferably from 0.01 to 1 g, more
preferably from 0.05 to 0.5 g, per 1 g of the prepolymer (B2-1).
When such a content is at least the lower limit within the above
range, the effect for improving water repellency and oil repellency
will be good, and when it is at most the upper limit, the heat
resistance will be good.
The number average molecular weight of the prepolymer (B2-1) is
within a range of from 1.times.10.sup.3 to 1.times.10.sup.5,
preferably from 1.5.times.10.sup.3 to 1.times.10.sup.5. Within such
a range, the coating properties of a prepolymer solution having
such a prepolymer dissolved in a solvent, are good, and a cured
product in a film form (a cured film) can easily be obtainable.
Further, the obtained cured film has good heat resistance,
mechanical properties, solvent resistance, etc.
In a case where the cured product of the prepolymer (B2-1) is
brittle, in order to improve the flexibility of the cured product,
a co-condensing component may be added at the time of producing the
prepolymer (B2-1). As such a co-condensing component, a compound
(Y-3) having two phenolic hydroxy groups other than (Y-1) may be
mentioned, which is capable of improving the flexibility of the
cured film.
Such a compound (Y-3) having two phenolic hydroxy groups, may, for
example, be a bifunctional phenol such as dihydroxybenzene,
dihydroxybiphenyl, dihydroxyterphenyl, dihydroxynaphthalene,
dihydroxyanthracene, dihydroxyphenanthracene,
dihydroxy-9,9-diphenylfluorene, dihydroxybenzofuran,
dihydroxydiphenyl ether, dihydroxydiphenyl thioether,
dihydroxybenzophenone, dihydroxy-2,2-diphenylpropane,
dihydroxy-2,2-diphenylhexafluoropropane or dihydroxybinaphthyl.
They may be used alone or in combination as a mixture of two or
more of them.
When an external energy such as heat, light or electron beam is
applied to the crosslinkable fluorinated aromatic prepolymer (B2)
such as the above prepolymer (B2-1), the crosslinkable functional
groups will react, and crosslinking or chain extension among the
prepolymer molecules will proceed to form a cured product.
At the time of curing the crosslinkable fluorinated aromatic
prepolymer (B2), for the purpose of increasing the reaction rate of
the crosslinking reaction or reducing the reaction defects, various
catalysts or additives may be used together with the crosslinkable
fluorinated aromatic prepolymer (B2).
For example, in a case where the crosslinkable fluorinated aromatic
prepolymer (B2) contains ethynyl groups or vinyl groups as
crosslinkable functional groups, the above catalysts may, for
example, be amines such as aniline, triethylamine,
aminophenyltrialkoxysilane and aminopropyltrialkoxysilane, or
organic metal compounds containing molybdenum, nickel, etc.
As the above additives, biscyclopentadienone derivatives are
preferred. A ethynyl group and a cyclopentadienone group
(1-oxocyclopenta-2,5-dien-3-yl group) will form an adduct by a
Diels-Alder reaction by heat, followed by a carbon
monoxide-removing reaction to form an aromatic ring. Accordingly,
when a biscyclopentadienone derivative is used, crosslinking or
chain extension can be carried out wherein an aromatic ring is a
linking moiety.
Specific examples of such biscyclopentadienone derivatives include,
for example,
1,4-bis(1-oxo-2,4,5-triphenyl-cyclopenta-2,5-dien-3-yl)benzene,
4,4'-bis(1-oxo-2,4,5-triphenyl-cyclopenta-2,5-dien-3-yl)biphenyl,
4,4'-bis(1-oxo-2,4,5-triphenyl-cyclopenta-2,5-dien-3-yl)1,1'-oxybisbenzen-
e,
4,4'-bis(1-oxo-2,4,5-triphenyl-cyclopenta-2,5-dien-3-yl)1,1'-thiobisben-
zene,
1,4-bis(1-oxo-2,5-di-[4-fluorophenyl]-4-phenyl-cyclopenta-2,5-dien-3-
-yl)benzene,
4,4'-bis(1-oxo-2,4,5-triphenyl-cyclopenta-2,5-dien-3-yl)1,1'-(1,2-ethaned-
iyl)bisbenzene and
4,4'-bis(1-oxo-2,4,5-triphenyl-cyclopenta-2,5-dien-3-yl)1,1'-(1,3-propane-
diyl)bisbenzene.
Among these biscyclopentadienone derivatives, entirely aromatic
skeleton biscyclopentadienone derivates are preferred from the
viewpoint of the heat resistance. They may be used alone or in
combination as a mixture of two or more of them.
The above-mentioned polyparaxylylene resin is a special polymer
which can be polymerized in a gas phase at a normal temperature.
For example, the polyparaxylylene resin is prepared by sublimating
a dimer shown below, at a temperature of about 160.degree. C.,
followed by thermal decomposition at 690.degree. C. to obtain a
monomer, which is introduced into a vacuum container (absolute
pressure of 4 Pa) at a normal temperature and polymerized on a
solid surface.
##STR00019##
The polyparaxylylene resin includes some types. Among them, one
having a molecular structure wherein chlorine is bonded to a
benzene ring (tradename: Parylene-C) has a relative dielectric
constant of 2.95 at a frequency of 1 MHz and has a characteristic
such that the dielectric breakdown strength and chemical resistance
are high, and thus it is suitable as the polymer compound (b).
Including such Parylene-C, examples of polyparaxylylenes useful as
the polymer compound (b) will be shown below. Here, below the
respective structural formulae, tradenames are shown.
##STR00020##
As the polymer compound (b), a thermosetting resin or an
ultraviolet curable resin may be employed from the viewpoint of
increasing the glass transition temperature or melting point. As
such a thermosetting resin or ultraviolet curable resin, a
polyimide, an epoxy resin or an acrylic resin may, for example, be
exemplified from the above examples, and from the viewpoint of the
above relative dielectric constant, a polyimide is more preferably
employed.
In a case where a polyimide is used as the polymer compound (b), a
polyimide precursor excellent in solubility in e.g. an organic
solvent is coated and thermally treated to convert the polyimide
precursor to a polyimide thereby to form the layer (B). As the
polyimide precursor, polyamic acid, or its ester may commonly be
used. When a polyimide precursor such as polyamic acid is heated to
a high temperature of from 200 to 350.degree. C., an imide
ring-closing reaction takes place, and it can be converted to a
thermally, chemically, electrically stable polyimide. In the
present invention, it is possible to employ a commonly commercially
available polyimide.
The polyimide precursor to be used in the present invention is
preferably a polyamic acid obtained by reacting a tetracarboxylic
acid dianhydride with a diamine compound, or its ester.
The tetracarboxylic acid dianhydride is not particularly limited,
and an aromatic tetracarboxylic acid dianhydride which is commonly
used for a polyimide synthesis may be used. Specifically,
3,3',4,4'-benzophenonetetracarboxylic dianhydride (BTDA),
3,3',4,4'-biphenyltetracarboxylic dianhydride,
2,3,3',4'-biphenyltetracarboxylic dianhydride, pyromellitic
dianhydride, 1,3-bis(2,3-dicarboxyphenoxy)benzene dianhydride,
1,4-bis(2,3-dicarboxyphenoxy)benzene dianhydride,
2,3,3',4'-benzophenonetetracarboxylic dianhydride,
2,2',3,3'-benzophenonetetracarboxylic dianhydride,
2,2',3,3'-biphenyltetracarboxylic dianhydride and
2,2',6,6'-biphenyltetracarboxylic dianhydride may, for example, be
mentioned.
As the diamine compound, an aromatic diamine compound is preferred.
The aromatic diamine compound is not particularly limited, and an
aromatic diamine compound commonly used for a polyamide synthesis
may be used. Specifically, 4,4'-diaminodiphenylmethane (DDM),
4,4'-diaminodiphenylether (DPE), 4,4'-bis(4-aminophenoxy)biphenyl
(BAPB), 1,4'-bis(4-aminophenoxy)benzene (TPE-Q),
1,3'-bis(4-aminophenoxy)benzene (TPE-R), o-phenylenediamine,
m-phenylenediamine, p-phenylenediamine, 3,4'-diaminodiphenyl ether,
4,4'-diaminodiphenyl sulfone, 3,4-diaminodiphenyl sulfone,
3,3'-diaminodiphenyl sulfone, 4,4'-methylene-bis(2-chloroanyline),
3,3'-dimethyl-4,4'-diaminobiphenyl, 2,6'-diaminotoluene,
2,4-diaminochlorobenzene, 3,3'-diaminobenzophenone,
3,4-diaminobenzophenone and 4,4'-diaminobenzophenone may, for
example, be mentioned.
The polymer compound (b) preferably has a glass transition
temperature or melting point of at least 80.degree. C., more
preferably at least 110.degree. C. When the glass transition
temperature or melting point is at least 80.degree. C., the
electret will be excellent in the heat resistance and charge
retention stability.
The weight average molecular weight of the polymer compound (b) is
preferably from 3,000 to 10,000,000, more preferably from 10,000 to
1,000,000.
The inorganic substance (c) may be suitably selected from known
inorganic substances, depending upon the desired relative
dielectric constant. Specifically, it is preferably at least one
member selected from the group consisting of a metal oxide, a metal
sulfide or a metal halide, and particularly from the viewpoint of
the relative dielectric constant, a metal oxide is suitably
employed.
The metal oxide may, for example, be silicon oxide, titanium oxide,
zirconium oxide, aluminum oxide, cerium oxide, calcium oxide,
magnesium oxide, tin oxide, manganese dioxide, nickel oxide,
chromium oxide, cobalt oxide, silver oxide, copper oxide, zinc
oxide, iron oxide, molybdenum oxide, barium titanate, strontium
titanate, or potassium niobate.
The metal sulfide may, for example, be zinc sulfide, aluminum
sulfide, potassium sulfide, silver sulfide, silicon sulfide, tin
sulfide, cerium sulfide, magnesium sulfide, copper sulfide, iron
sulfide, or molybdenum sulfide.
The metal halide may, for example, be silver fluoride, calcium
fluoride, cerium fluoride, copper fluoride, barium fluoride,
magnesium fluoride, lithium fluoride, copper chloride, silver
chloride, calcium chloride, zirconium chloride, tin chloride,
cerium chloride, silver bromide, cobalt bromide, cesium bromide or
copper bromide.
Among them, a metal oxide is preferred, and from the viewpoint of
electret properties, at least one member selected from the group
consisting of silicon oxide, titanium oxide, zirconium oxide,
aluminum oxide, cerium oxide, tin oxide, manganese dioxide, nickel
oxide, iron oxide and barium titanate is preferred, and
particularly preferred is silicon oxide.
The layer (B) may be one containing the polymer compound (b) or one
containing the inorganic substance (c).
The method for forming the layer (B) is not particularly limited,
and a conventional film-forming method may be used depending upon
the material to be used.
For example, in a case where the polymer compound (b) is to be
used, film forming may be carried out by a wet coating method, or
film forming may be carried out by press-forming a film. Otherwise,
film forming may be carried out by a dry process such as vapor
deposition, CVD or sputtering. Particularly from the viewpoint of
the film forming process, film forming is preferably carried out by
a wet coating method.
In a case where the layer (B) is to be formed by a wet coating
method, as the polymer compound (b), one having a solubility such
that it is soluble in a solvent, preferably soluble at a
concentration of at least 5 mass % in a solvent to be used at
25.degree. C., is used. If such a solubility is less than 5 mass %,
it tends to be difficult to obtain a good coating film. Such a
solubility is preferably at least 10 mass %, more preferably at
least 15 mass %. The upper limit of the solubility is preferably 50
mass %, more preferably 30 mass % in consideration of deterioration
of the filtration property or film forming property by an increase
of the solution viscosity.
The film forming of the layer (B) by a coating method can be
carried out by the same method as the method for film forming the
coating film as mentioned as the method for forming the layer (A).
That is, it can be carried out by dissolving the polymer compound
(b) in a solvent to prepare a coating composition, and coating the
surface of a substrate or the layer (A) with the coating
composition, followed by drying by e.g. baking.
To such a coating composition, a silane coupling agent may be
incorporated. A coating film (layer (B)) formed by using such a
coating composition will be excellent in adhesion to the substrate
or the layer (A). As such a silane coupling agent, the same one as
described above may be employed.
Further, as the coating composition, one having a prepolymer of the
polymer compound (b) dissolved in a solvent may be prepared, and
such a coating composition is applied to the surface of a substrate
or the layer (A) and then cured by applying an external energy such
as heat, light or electron beam to obtain the layer (B) as a cured
film.
In a case where the inorganic substance (c) is used, the layer (B)
may be formed by a wet method such as a coating method or a sol gel
method, or may be formed by a dry process such as a sputtering
method, a vapor deposition method or a CVD method.
Now, a case where a silicon oxide film is to be formed by a wet
method, will be described. For example, a method is preferably
employed wherein a hydrolyzable silane compound such as a
tetraalkoxy silane or an alkyltrialkoxy silane, a partially
hydrolyzed condensate of a hydrolyzable silane compound, a
polysilazane or the like is dissolved in the above-mentioned protic
solvent or aprotic solvent, followed by coating and baking in the
atmospheric air to form a silicon oxide film. In a case where a wet
method is employed, the method is preferably carried out in a
non-aqueous system from the viewpoint of the electret properties.
As a film forming method in a non-aqueous system, in a case where a
silicon oxide film is to be formed, a method is preferably employed
wherein a xylene solution of polysilazane is coated and fired in
the atmospheric air to form a silicon oxide film. The firing
temperature in this case is preferably from 150.degree. C. to
600.degree. C., more preferably from 180.degree. C. to 450.degree.
C. with a view to preventing cracking due to a difference in the
linear expansion coefficient from the layer (A).
Now, the above polysilazane will be described in detail.
The polysilazane is a polymer having at least two repeating units
represented by (--Si--N--), and in this chemical formula, to the
remaining two bonds of the silicon atom (tetravalent) and to the
remaining one bond of the nitrogen atom (trivalent), a hydrogen
atom or an organic group (such as an alkyl group) is bonded. The
polysilazane is not limited to a polymer of a chain structure
composed solely of the above repeating unit, but may be a polymer
wherein one or both of the above-mentioned remaining two bonds of
the silicon atom are bonded to the above bond of the nitrogen atom
to form a cyclic structure. Such a polymer may be composed solely
of repeating units of such a cyclic structure or may be a chain
form polymer partially having such a cyclic structure.
As the polysilazane in the present invention, a polysilazane or
modified polysilazane disclosed in e.g. JP-A-9-31333 or in
references disclosed in such publication may be used.
The polysilazane will be decomposed in the presence of oxygen, and
nitrogen atoms are substituted by oxygen atoms to form silicon
oxide (also called silica). The silicon oxide film formed from such
a polysilazane is more dense as compared with a silicon oxide film
formed from the above-mentioned hydrolyzable silane compound. For
example, the silicon oxide film formed from perhydropolysilazane is
more dense as compared with a silicon oxide film formed from a
tetrafunctional hydrolyzable silane compound such as a
tetraalkoxysilane and is excellent in the surface properties such
as abrasion resistance and in the charge retention performance and
heat resistance when formed into an electret.
In order to cure the polysilazane to form a silicon oxide film,
heating so-called firing is usually required. However, in the
present invention, the firing temperature is restricted, since it
is necessary to laminate the layer (B) on the layer (A) containing
the polymer compound (a). That is, it is difficult to carry out
curing by heating to a temperature higher than the heat resistance
temperature of the polymer compound (a). Therefore, in some cases,
it will be necessary to cure the polysilazane at a temperature
lower than the heat resistance temperature of the polymer compound
(a).
Usually, as the temperature for firing the polysilazane in the
present invention, a temperature lower than the heat resistance
temperature of the polymer compound (a) constituting the layer (A)
to be laminated with the layer (B), is employed, and the upper
limit of the temperature is usually 400.degree. C. In order to
prevent formation of cracks due to the difference in the linear
expansion coefficient from the layer (A), the firing temperature is
preferably at most 200.degree. C.
Further, as an atmosphere for the firing, an atmosphere in which
oxygen is present, such as air, is preferred. By the firing of the
polysilazane, its nitrogen atoms will be substituted by oxygen
atoms to form a silicon oxide film. By carrying out the firing in
an atmosphere wherein sufficient oxygen is present, a dense silicon
oxide layer will be formed. Further, treatment with water or steam
is also useful for the curing at a low temperature (see
JP-A-7-223867).
In order to lower the temperature for firing the polysilazane, a
catalyst is usually employed. Depending upon the type or amount of
the catalyst, the polysilazane can be fired at a low temperature,
and in some cases, curing can be carried out at room temperature
without requiring the firing.
As the catalyst, it is preferred to employ a catalyst capable of
firing and curing the polysilazane at a lower temperature. As such
a catalyst, a metal catalyst containing fine particles of a metal
such as gold, silver, palladium, platinum or nickel
(JP-A-7-196986), an amine, an acid (JP-A-9-31333), etc. may, for
example, be mentioned. The amine may, for example, be an
alkylamine, a dialkylamine, a trialkylamine, an arylamine, a
diarylamine or a cyclic amine. The acid may, for example, be an
organic acid such as acetic acid, or an inorganic acid such as
hydrochloric acid.
The average particle size of the fine particles of the metal
catalyst is preferably smaller than 0.1 .mu.m, more preferably
smaller than 0.05 .mu.m in order to secure the transparency of the
cured product. In addition, as the average particle size becomes
small, the specific surface area increases, and the catalyst
stability increases, and thus from the viewpoint of the improvement
of the catalytic performance, the metal catalyst having a smaller
average particle size is preferred.
The amine or acid may also be incorporated to the polysilazane
solution. Otherwise the curing can be accelerated by contacting a
solution of the amine or acid (including an aqueous solution) or
its vapor (including the vapor from the aqueous solution) with the
polysilazane.
In a case where the catalyst is used as incorporated to the
polysilazane, the amount of the catalyst to be incorporated is
preferably from 0.01 to 10 parts by mass, more preferably from 0.05
to 5 parts by mass, per 100 parts by mass of the polysilazane. If
the amount to be incorporated is less than 0.01 part by mass, no
adequate catalyst effects can be expected, and if it exceeds 10
parts by mass, agglomeration of the catalyst itself is likely to
take place, thereby impairing the electrical insulation property,
transparency, etc.
<Laminate>
The laminate in the present invention comprises the directly
laminated layers (A) and (B) as the essential constituting units.
Further, in the present invention, the layer (A) is disposed on the
outermost surface on a side opposite to the side where electric
charge is injected at the time of injecting electric charge to the
laminate to form an electret. Further, the laminate may have, as
the layer (A), a layer (A) disposed at a position other than the
outermost surface.
The laminate may be constituted solely by the layers (A) and (B) or
may contain another layer. Such another layer may, for example, be
a metal layer or an organic monomolecular film layer by e.g. the
above-mentioned silane coupling agent. Such a layer can be formed
by a conventional method.
From the viewpoint of the film forming process, the laminate is
preferably a (n.sub.A+n.sub.B) layered laminate wherein n.sub.A
layers of layer (A) and n.sub.B layers of layer (B) are alternately
laminated. Here, n.sub.A is an integer of from 1 to 5, n.sub.B is
an integer of from 1 to 5, and the value of n.sub.A-n.sub.B is 0 or
1. Particularly, n.sub.A is preferably from 1 to 2, n.sub.B is also
preferably 1 or 2, and the value of n.sub.A-n.sub.B is preferably
0.
Preferred specific examples of the laminate may, for example, be a
two-layered laminate wherein from a side opposite to the side where
electric charge is injected, the layer (A) and the layer (B) are
laminated in this order (hereinafter referred to as layer (A)/layer
(B), the same applies to other laminates); a three-layered laminate
of layer (A)/layer (B)/layer (A); a four-layered laminate of layer
(A)/layer (B)/layer (A)/layer (B), etc.
The shape and size of the laminate may suitably be set depending
upon the shape and size of the desired electret. An electret is
usually employed in the form of a film having a thickness of from 1
to 200 .mu.m, and the laminate is preferably a film having a
thickness of from 1 to 200 .mu.m. The thickness of such a laminate
is preferably from 3 to 50 .mu.m, particularly preferably from 5 to
20 .mu.m, since such a thickness is advantageous for the
processability and the properties as an electret.
Further, in the laminate, the thickness of the layer (B) (thickness
per one layer) is at least 1 .mu.m. When the thickness of the layer
(B) (thickness per one layer) is within this range, the surface
charge density of an electret is high. Such a thickness is
preferably at least 1.5 .mu.m, more preferably at least 2 .mu.m,
whereby the above effect will be excellent. The upper limit of such
a thickness is preferably 20 .mu.m, more preferably 10 .mu.m from
the viewpoint of the film-forming process and improvement of the
surface charge density.
The thickness of the layer (A) (thickness per one layer) is not
particularly limited and may be suitably set in consideration of
the entire thickness of the laminate, the number of layers (A),
etc. in consideration of the charge retention performance, heat
resistance, etc. of the electret, the thickness of the layer (A)
(thickness per one layer) is preferably from 3 to 50 .mu.m, more
preferably from 5 to 20 .mu.m. The thickness of each of the layer
(A) and the layer (B) as well as the entire thickness of the
laminate, can be measured by an optical interferotype film
thickness measuring apparatus.
The laminate can be formed by sequentially laminating a layer (A)
and a layer (B) on a substrate so that the layer (A) will be in
contact directly with the substrate. For example, a double layered
laminate can be formed by firstly forming a layer (A) on a
substrate and then laminating a layer (B) on the layer (A).
Further, in the case of a at least three-layered laminate, by
laminating a layer (A) and a layer (B) sequentially and alternately
depending upon the desired number of laminated layers, from the
substrate side, it is possible to form a laminate having a desired
number of laminated layers. At that time, another layer may
optionally be laminated, but the laminate contains a laminate
wherein at least a layer (A) and a layer (B) are directly
laminated. And, the layer (A) is disposed on the outermost surface
on a side opposite to the side where electric charge is
injected.
As a substrate, it is possible to employ a substrate which can be
connected to earth when electric charge is injected to the obtained
laminate, without selecting the material. As a preferred material,
a conductive metal such as gold, platinum, copper, aluminum,
chromium or nickel may be mentioned. Further, a material other than
a conductive metal, such as an insulating material such as an
inorganic material of e.g. glass or an organic polymer material
such as polyethylene terephthalate, polyimide, polycarbonate or an
acrylic resin may also be used so long as it is one having its
surface coated with a metal film by a method such as sputtering,
vapor deposition or wet coating.
Further, a semiconductor material such as silicon may also be used
as a substrate so long as it is one having a similar surface
treatment applied, or the ohmic value of the semiconductor material
itself is low. The ohmic value of the substrate material is
preferably at most 0.1 .OMEGA.cm, particularly preferably at most
0.01 .OMEGA.cm, by volume resistivity.
Such a substrate may be a flat plate having a smooth surface or one
having convexoconcave formed thereon. Otherwise, it may have
patterning applied in various shapes. Particularly in a case where
the above-mentioned insulating substrate is employed, a pattern or
convexoconcave may be formed on the insulating substrate itself, or
a pattern or convexoconcave may be formed on a metal film coated on
the surface.
As a method for forming a pattern or convexoconcave on the
substrate, a conventional method may be employed without any
particular restriction. As the method for forming a pattern or
convexoconcave, either a vacuum process or a wet process may be
employed. As specific examples of such a method, a vacuum process
may, for example, be a sputtering method via a mask or a vapor
deposition method via a mask, and a wet process may, for example,
be a roll coater method, a casting method, a dipping method, a spin
coating method, a casting-on-water method, a
Langmuir.cndot.Blodgett method, a die coating method, an ink jet
method or a spray coating method. Otherwise, it is possible to
employ a printing technique such as a relief printing method, a
gravure printing method, a lithography method, a screen printing
method or a flexo printing method. Further, as a method for forming
a fine pattern or convexoconcave, a nanoimprinting method or a
photolithography method may, for example, be employed.
As a method for laminating the layers (A) and (B) as well as
another layer, film forming by the above-described coating method
or the like may simply be repeated, or during repetition of the
film forming, surface treatment may be applied to the
undercoating.
As such surface treatment, it is possible to employ a method of
applying the above-mentioned silane coupling agent or a method of
roughening or presenting hydrophilicity to the surface by plasma
treatment.
In the case of applying the silane coupling agent, such surface
treatment can be carried out by dissolving the above-mentioned
silane coupling agent in the above-mentioned protic solvent,
aprotic solvent or protic fluorinated solvent, followed by coating
by the same coating method as described above.
Further, in the case of roughening or presenting hydrophilicity to
the surface by plasma treatment, it is possible to employ plasma
treatment using a gas such as oxygen, nitrogen, argon, methane,
CHF.sub.3 or CF.sub.4. Such gases may be used alone or in suitable
combination as a mixture. In such plasma treatment, to minimize the
decrease of the underlayer film thickness, it is preferred to
employ oxygen, nitrogen, argon, methane gas or a gas mixture
thereof.
In a case where a copper substrate, a low resistance silicon
substrate or the like is used as a substrate having a low
resistance, it is possible to inject electric charge to the
laminate to form an electret without removing, from the substrate,
the laminate formed on the substrate, as described hereinafter.
As described above, in the laminate prepared by sequentially
laminating the layer (A) and the layer (B) on the substrate, the
layer (A) is in contact with the substrate. Therefore, at the time
of injecting electric charge to the laminate on the substrate to
form an electret as mentioned above, the layer (A) is disposed on
the outermost surface on a side opposite to the side where electric
charge is injected, of the laminate. As the layer (A) is so
disposed, the effects of the present invention can be sufficiently
obtained.
Further, one disposed on the outermost surface on the side where
electric charge is injected, of the laminate, may be the layer (A)
or the layer (B). It is preferred that the layer (B) is disposed on
the outermost surface on the side where electric charge is
injected, of the laminate, since the effects of the present
invention will be thereby excellent.
The electret of the present invention can be produced by injecting
electric charge to the above-described laminate.
As a method for injecting electric charge to the laminate, it is
usually possible to employ any method so long as it is a method to
charge an insulator. For example, it is possible to use a corona
discharge method, an electron beam bombardment method, an ion beam
bombardment method, a radiation method, a light irradiation method,
a contact charging method or a liquid contact charging method, as
disclosed in G. M. Sessler, Electrets Third Edition, pp. 20,
Chapter 2.2, "Charging and Polarizing Methods" (Laplacian Press,
1998) (hereinafter referred to as Non-Patent Document 1).
Especially, for the electret of the present invention, it is
preferred to employ a corona discharge method or an electron beam
bombardment method.
Further, as a temperature condition at the time of injecting
electric charge, it is preferred to carry out the injection at a
temperature of at least the glass transition temperature of the
polymer compound (a) from the viewpoint of the stability of
electric charge maintained after the injection, and it is
particularly preferred to carry out the injection under a
temperature condition of about the glass transition
temperature+from 10 to 20.degree. C. Further, the voltage to be
applied at the time of injecting electric charge is preferably high
so long as it is lower than the dielectric breakdown voltage of the
laminate. The voltage applied to the laminate in the present
invention is from 6 to 30 kV, preferably from 8 to 15 kV in the
case of positive charge, and it is from -6 to -30 kV, preferably
from -8 to -15 kV in the case of negative charge. The polymer
compound (a) is capable of maintaining a negative electric charge
more stably than a positive electric charge, and accordingly, it is
further preferred to apply a voltage of from -8 to -15 kV.
After injection of the electric charge, the electret may be used as
it is together with the substrate for an electrostatic induction
conversion device, or it may be removed from the substrate and then
used for an electrostatic induction conversion device.
The electret of the present invention is suitable as an
electrostatic induction conversion device to convert electric
energy to kinetic energy.
Such an electrostatic induction conversion device may, for example,
be a vibration-type power-generating unit, an actuator or a sensor.
The structure of such an electrostatic induction conversion device
may be the same as a conventional one except that as the electret,
the electret of the present invention is used.
As compared with conventional electrets, the electret of the
present invention is capable of making the surface charge density
high and has a high surface voltage. Therefore, the electrostatic
induction conversion device using such an electret has an improved
efficiency for conversion between electric energy and kinetic
energy and exhibits an excellent performance.
The reason as to why such effects can be obtained, is not clearly
understood. However, it is considered that to the layer (A) playing
a role of electric charge retention, the layer (B) different in the
relative dielectric constant is laminated in a prescribed film
thickness, whereby internal polarization results by Maxwell-Wagner
effects (see Non-Patent Document 1, p. 25), and electric charge
separation is promoted in the electret film, and at the same time,
it is possible by the layer (B) to prevent electric charge
maintained in the layer (A) from flowing out of the electret
film.
EXAMPLES
Now, specific cases of the above embodiment will be described as
Examples. However, it should be understood that the present
invention is by no means restricted to the following Examples.
The relative dielectric constants of materials used in each of the
following Examples are all values disclosed in brochures (values
measured in accordance with ASTM D150 at a frequency of 1 MHz).
The volume resistivity is a value measured in accordance with ASTM
D257.
The dielectric breakdown voltage is a value measured in accordance
with ASTM D149.
The intrinsic viscosity [.eta.](30.degree. C.) (unit: dl/g) is a
value measured by an Ubbelohde Viscometer at 30.degree. C. by using
perfluoro(2-butyltetrahydrofuran) as a solvent.
Further, in each of the following Examples, as a substrate to form
an electret, a low resistance silicon substrate (volume resistivity
of from 0.003 to 0.007 .OMEGA.cm) was used. In the following
Examples, such a substrate is referred to as a "silicon
substrate".
Further, in each of the following Examples, for the measurement of
the thickness of each layer was carried out by using optical
interferotype film thickness measuring apparatus C10178
manufactured by Hamamatsu Photonics K.K.
Preparation Example 1
Preparation of Polymer Composition Solution M1
(1) Preparation of Polymer Solution
45 g of perfluorobutenyl vinyl ether
(CF.sub.2.dbd.CFOCF.sub.2CF.sub.2CF.dbd.CF.sub.2), 240 g of
deionized water, 16 g of methanol and 0.2 g of diisopropylperoxy
dicarbonate powder (((CH.sub.3).sub.2CHOCOO).sub.2) as a
polymerization initiator, were introduced into a pressure resistant
glass autoclave having an internal capacity of 1 L. The interior of
the system was replaced three times with nitrogen, and then,
suspension polymerization was carried out at 40.degree. C. for 23
hours. As a result, 40 g of polymer A1 was obtained. The infrared
absorption spectrum of this polymer was measured, whereby
absorption in the vicinity of 1,660 cm.sup.-1 or 1,840 cm.sup.-1
attributable to the double bond present in the monomer, was not
detected.
Polymer A1 was subjected to heat treatment at 250.degree. C. for 8
hours in air and then immersed in water to obtain polymer A2 having
--COOH groups as terminal groups. The infrared absorption spectrum
of a compression-molded film of the polymer was measured, whereby
the characteristic absorption at 1,775 and 1,810 cm.sup.-1
attributable to --COOH groups was observed. Further, the intrinsic
viscosity [.eta.](30.degree. C.) of this polymer was 0.24 dl/g.
The volume resistivity of polymer A2 was >10.sup.17 .OMEGA.cm,
the dielectric breakdown voltage was 19 kV/mm, and the relative
dielectric constant was 2.1.
With respect to polymer A2, the differential scanning calorimetery
(DSC) was carried out, whereby the glass transition temperature
(Tg) of polymer A2 was 108.degree. C.
In a perfluorotributylamine, the above polymer A2 was dissolved at
a concentration of 15 mass % to obtain a polymer solution P1.
(2) Incorporation of Silane Coupling Agent
A solution having 10.6 g of perfluorotributylamine added to 84.6 g
of the above polymer solution P1, and a silane coupling agent
solution having 0.4 g of .gamma.-aminopropylmethyldiethoxysilane
dissolved in 4.7 g of 2-(perfluorohexyl)ethanol, were mixed to
obtain a uniform polymer composition solution M1.
Example 1
Production of Electret A
On a silicon substrate of 3 cm.times.3 cm having a thickness of 350
.mu.m, the polymer composition solution M1 was applied by a spin
coating method and dried by baking at 200.degree. C. to form a
coating film having a thickness of 10 .mu.m (hereinafter referred
to as a coating film A). Then, N.sub.2 plasma treatment was applied
on the surface of this coating film A by using REACTIVE ION ETCHING
SYSTEM RIE-10NR manufactured by SAMCO International, Inc. Then, on
the coating film A, an N-methylpyrrolidone (NMP) solution
containing 12 mass % of a polyamic acid (Semicofine SP483,
manufactured by Toray Industries, Inc., relative dielectric
constant after polyimidation: 3.75, glass transition temperature:
at least 350.degree. C.) was applied by a spin coating method,
followed by heat treatment at 200.degree. C. for 5 hours for
polyimidation thereby to obtain a laminate film A having a total
film thickness of 15 .mu.m [double layered laminate having 10 .mu.m
of layer (A)/5 .mu.m of layer (B) laminated in this order from the
substrate side].
To the obtained laminate film A, electric charge was injected by
corona discharge to obtain an electret A. The injection of electric
charge was carried out by using a corona charging equipment, of
which a schematic construction diagram is shown in FIG. 1, by the
following procedure under a condition of 120.degree. C. at a
charging voltage of -8 kV for a charging time of 3 minutes. That
is, by using a substrate (a silicon substrate in this Example) (10)
as an electrode, a high voltage of -8 kV was applied between a
corona needle (14) and the substrate (10) by a DC high voltage
power source (12) (HAR-20R5, manufactured by Matsusada Precision
Inc.) to inject electric charge to the laminate (11) formed on the
substrate (10). In this corona charging equipment, negative ions
discharged from the corona needle (14) are homogenized by a grid
(16) and then showered down on the laminate (11), whereby electric
charge is injected. Here, to the grid (16), a voltage of -600 V is
applied from the power source (18) for grid.
Example 2
Production of Electret B
On a silicon substrate of 3 cm.times.3 cm having a thickness of 350
.mu.m, a coating film A having a thickness of 14 .mu.m was formed
in the same manner as in Example 1. Then, on the surface of the
coating film A, N.sub.2 plasma treatment was carried out by the
same procedure as in Example 1. Then, in the same manner as in
Example 1, on the coating film A, a polyimide film was formed in a
film thickness of 1 .mu.m to obtain a laminate film B having a
total film thickness of 15 .mu.m [double layered laminate having 14
.mu.m of layer (A)/1 .mu.m of layer (B) laminated in this order
from the substrate side].
To the obtained laminate film B, electric charge was injected by
the same procedure as in Example 1 to obtain an electret B.
Example 3
Production of Electret C
On a silicon substrate of 3 cm.times.3 cm having a thickness of 350
.mu.m, a coating film A having a thickness of 10 .mu.m was formed
in the same manner as in Example 1. Then, on this coating film A, a
polyparaxylylene resin (Parylene C, manufactured by Parylene Japan,
relative dielectric constant: 2.95, glass transition temperature:
87 to 97.degree. C.) was chemically vapor-deposited by a CVD method
to form a film, thereby to obtain a laminate film C having a total
film thickness of 15 .mu.m [double layered laminate having 10 .mu.m
of layer (A)/5 .mu.m of layer (B) laminated in this order from the
substrate side].
To this laminate film C, electric charge was injected by the same
procedure as in Example 1 to obtain an electret C.
Example 4
Production of Electret D
On a silicon substrate of 3 cm.times.3 cm having a thickness of 350
.mu.m, a coating film A having a thickness of 13 .mu.m was formed
in the same manner as in Example 1. Then, on the surface of this
coating film A, N.sub.2 plasma treatment was carried out by the
same procedure as in Example 1. Then, a xylene solution containing
20 mass % of polysilazane (DEN-3, manufactured by Clariant) was
applied by a spin coating method, followed by baking at 200.degree.
C. for 12 hours to form a silicon oxide film (relative dielectric
constant after baking: 2.6) on the coating film A thereby to obtain
a laminate film D having a total film thickness of 15 .mu.m [double
layered laminate having 13 .mu.m of layer (A)/2 .mu.m of layer (B)
laminated in this order from the substrate side].
To this laminate film D, electric charge was injected by the same
procedure as in Example 1 to obtain an electret D.
Comparative Example 1
Production of Electret E
On a silicon substrate of 3 cm.times.3 cm having a thickness of 350
.mu.m, a coating film A having a thickness of 14.5 .mu.m was formed
in the same manner as in Example 1. Then, on the surface of the
coating film A, N.sub.2 plasma treatment was carried out by the
same procedure as in Example 1. Then, in the same manner as in
Example 1, a polyimide film was formed on the coating film A to
obtain a laminate film E having a total film thickness of 15 .mu.m
[double layered laminate having 14.5 .mu.m of layer (A)/0.5 .mu.m
of layer (B) laminated in this order from the substrate side].
To this laminate film E, electric charge was injected by the same
procedure as in Example 1 to obtain an electret E.
Comparative Example 2
Production of Electret F
On a silicon substrate of 3 cm.times.3 cm having a thickness of 350
.mu.m, a coating film A having a thickness of 10 .mu.m was formed
in the same manner as in Example 1. Then, on the surface of the
coating film A, N.sub.2 plasma treatment was carried out by the
same procedure as in Example 1. Then, a m-xylene solution
containing 15 mass % of a cycloolefin polymer (ZEON EX480,
manufactured by ZEON CORPORATION, relative dielectric constant:
2.3, glass transition temperature: 138.degree. C.) was applied by a
spin coating method, followed by drying by baking at 160.degree. C.
for one hour to obtain a laminate film F having a total film
thickness of 15 .mu.m [double layered laminate having 10 .mu.m of
layer (A)/5 .mu.m of layer (B) laminated in this order from the
substrate side].
To this laminate film F, electric charge was injected by the same
procedure as in Example 1 to obtain an electret F.
Example 5
Production of Electret G
On a silicon substrate of 3 cm.times.3 cm having a thickness of 350
.mu.m, a coating film A having a thickness of 7 .mu.m was formed in
the same manner as in Example 1. Then, on the surface of the
coating film A, N.sub.2 plasma treatment was carried out by the
same procedure as in Example 1. Then, in the same manner as in
Example 1, a polyimide film was formed in a thickness of 2 .mu.m on
the coating film A to obtain a laminate film having a total film
thickness of 9 .mu.m. Further, on this laminate film, the polymer
composition solution M1 was applied by a spin coating method,
followed by drying by baking at 200.degree. C. to obtain a laminate
film G having a total film thickness of 15 .mu.m [three-layered
laminate having 7 .mu.m of layer (A)/2 .mu.m of layer (B)/6 .mu.m
of layer (A) laminated in this order from the substrate side].
To this laminate film G, electric charge was injected by the same
procedure as in Example 1 to obtain an electret G.
Example 6
Production of Electret H
On a silicon substrate of 3 cm.times.3 cm having a thickness of 350
.mu.m, a coating film A having a thickness of 7 .mu.m was formed in
the same manner as in Example 1. Then, on the surface of the
coating film A, N.sub.2 plasma treatment was carried out by the
same procedure as in Example 1. Then, in the same manner as in
Example 1, a polyimide film was formed in a thickness of 2 .mu.m on
the coating film A to obtain a laminate film having a total film
thickness of 9 .mu.m. Further, on the laminate film, the polymer
composition solution M1 was applied by a spin coating method,
followed by drying by baking at 200.degree. C. to obtain a laminate
film having a total film thickness of 13 .mu.m. Further, on the
surface of the laminate film, N.sub.2 plasma treatment was carried
out by the same procedure as in Example 1, and in the same manner
as in Example 1, a polyimide film was formed in a thickness of 2
.mu.m thereon to obtain a laminate film H having a total film
thickness of 15 .mu.m [four-layered laminate having 7 .mu.m of
layer (A)/2 .mu.m of layer (B)/4 .mu.m of layer (A)/2 .mu.m of
layer (B) laminated in this order from the substrate side].
To this laminate film H, electric charge was injected by the same
procedure as in Example 1 to obtain an electret H.
Comparative Example 3
Production of Electret I
On a silicon substrate of 3 cm.times.3 cm having a thickness of 350
.mu.m, a coating film A having a thickness of 15 .mu.m was formed
in the same manner as in Example 1 and designated as a coating film
I.
To this coating film I, electric charge was injected by the same
procedure as in Example 1 to obtain an electret I.
Test Example 1
Charging Test
With respect to the electrets A to I obtained as described above,
charging tests were carried out by the following procedure.
The electrets A to I immediately after injecting electric charge by
corona charging under conditions of a charging voltage of -8 kV and
a charging time of 3 minutes, were, respectively, returned to room
temperature (25.degree. C.), and their surface voltages (initial
surface voltages) and surface charge densities (initial surface
charge densities) were measured. Further, the respective electrets
were stored for 200 hours under conditions of 20.degree. C. and 60%
RH and then returned to room temperature, and their surface
voltages (surface voltages after 200 hours) and surface charge
densities (surface charge densities after 200 hours) were measured.
The results are shown in Table 1.
The surface voltage (V) was obtained by measuring surface voltages
at 9 measuring points (set in a lattice arrangement for every 3 mm
from the center of the film, as shown in FIG. 2) of each electret
by using a surface voltmeter (model 279, manufactured by Monroe
Electronics Inc.), and taking their average value. The surface
charge density .sigma.(mC/m.sup.2) was obtained by using the
following formulae.
<In the Case of Double-Layered Film> .sigma.=.di-elect
cons..sub.0V/[(d.sub.1/.di-elect cons..sub.r1)+(d.sub.2/.di-elect
cons..sub.r2)] wherein .di-elect cons..sub.0: dielectric constant
in vacuum, .di-elect cons..sub.r1, .di-elect cons..sub.r2: relative
dielectric constants of the respective layers, V: surface voltage
(V), d.sub.1, d.sub.2: sum (m) of thicknesses of the respective
layers. <In the Case of Single Layered Film>
.sigma.=.di-elect cons..sub.r.di-elect cons..sub.0V/d wherein
.di-elect cons..sub.0: dielectric constant in vacuum, .di-elect
cons..sub.r0: relative dielectric constant of the single layer, V:
surface voltage (V), d: film thickness (m) of single layer.
TABLE-US-00001 TABLE 1 Surface charge density Relative dielectric
Film thickness Surface voltage (V) (mC/m.sup.2) constant of layer
of layer (B) Difference in relative After 200 After 200 Electret
(B) (.mu.m) dielectric constant Initial hours Initial hours A 3.75
5 1.65 -2.265 -1.863 -3.376 -2.777 B 3.75 1 1.65 -1.694 -1.674
-2.085 -2.060 C 2.95 5 0.85 -2.270 -2.086 -3.120 -2.867 D 2.6 2 0.5
-1.669 -1.542 -1.774 -1.639 E 3.75 0.5 1.65 -1.205 -1.170 -1.512
-1.468 F 2.3 5 0.2 -1.306 -1.256 -1.595 -1.534 G 3.75 2 1.65 -1.407
-1.372 -1.785 -1.741 H 3.75 2 1.65 -1.697 -1.559 -2.395 -2.200 I --
-- -- -1.277 -1.274 -1.583 -1.579
From the results in Table 1, judging from the surface voltages and
surface charge densities at the initial stage and after 200 hours,
electrets A to D, G and H showed an improvement in the surface
voltage and surface charge density, as compared with electrets E, F
and I. Further, these values were found to be higher as the
difference in the relative dielectric constant was larger.
INDUSTRIAL APPLICABILITY
The electret of the present invention is capable of increasing the
surface charge density and has a high surface voltage, and an
electrostatic induction conversion device using such an electret
has an improved efficiency for conversion between electric energy
and kinetic energy and thus is useful for e.g. a vibration type
power generator, an actuator, a censor, etc. having excellent
performance.
The entire disclosure of Japanese Patent Application No.
2008-082532 filed on Mar. 27, 2008 including specification, claims,
drawings and summary is incorporated herein by reference in its
entirety.
* * * * *